54  c 


Clark 

Chemical  Study  of  the 
Enrichment  of  copper  sulfide  Ores 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


H»  RALPH  B.  REED  LIBRARY 

OKNIA 
:.IF* 


- 


Bulletin  University  of  [NewJMexico, 


WHOLE  NUMBER  75 


Chemistry  Series  Albuquerque.  N.  M.,  June.  1914 


Vol.  I.    No.  2 


A  Chemical  Study  of  the  Enrichment 
of  Copper  Sulfide  Ores 


A  DISSERTATION 


Subinitted-to-the  Dep 


rf-Ch 


d  to  the 

Committee  on  Gradate  Study  of  Ihe  Leland  Stanford 
Junior  University  in  partial  fulfillment  of  the  require- 
ments for  the  degree  of  Doctor  of  Philosophy 

>GY 

I  -1A 

XJF. 


BY 


fL 


JOHN  DUSTIN  GLA-B 


GEOLOGY  LIBRARY 
GEOL.  BLDG.  4372 


CRYSTALS  OF  CUPRO-CUPRIC  SULFITE 

X    50 
See  experiment  Xo.  10. 


CHALCOCITE   CRYSTAL 

X    200 
See  experiment   No.  41. 


Geology 
Library 


Since  the  time  recorded  in  our  earliest  history  me- 
tallic ores  have  been  taken  from  mines  and  deposits. 
Undoubtedly  the  first  discovered  deposits  were  found 
by  accident.  The  mining  of  the  ore  probably  followed 
well  defined  veins  and  stopped  when  such  were  ex- 
hausted. The  work  of  the  ignorant  prospector  of  to-day 
is  much  like  the  probable  simple  procedure  of  the 
ancients. 

Observations  which  have  led  to  the  science  of  Geol- 
ogy must  have  made  some  miners  proficient  in  predict- 
ing the  occurrence  of  mineral  bearing  veins,  etc.  It  is 
certain  that  to-day  the  mining  engineer  and  mining 
geologist  can,  as  a  result  of  training  and  observation, 
"see  beneath  the  ground",  and  can  successfully  direct 
development  work  carried  on  to  locate  valuable  metal- 
bearing  bodies. 

The  engineer  and  geologist  has  made  use  of  many 
of  the  sciences  in  conducting  his  work.  Chemistry  has 
always  played  an  important  part,  and  it  seems  that  its 
field  of  usefulness  has  only  been  entered  upon.  It  ap- 
pears that  the  results  of  purely  theoretical  and  experi- 
mental laboratory  work  in  chemistry  may  be  of  the  most 
practical  importance  when  given  to  these  mining  ex- 


987??? 


8Q  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

perts.  This  much  is  certain,  that  for  understanding  en- 
richment in  our  copper  mines  much  chemical  work  is 
necessary,  as  may  be  seen  when  an  authority  like  W.  H. 
Emmons1  says,  (in  his  publication,  "Enrichment  of 
Sulfide  Ores",)  "To  the  chemist  this  paper  is  an  appeal 
for  more  experimental  data  on' the  important  mineral 
syntheses  involved  in  the  processes." 

DEFINITIONS  OF  ENRICHMENT. 

The  meaning  of  downward  secondary  enrichment 
and  a  summary  of  much  of  the  field  observation,  lab- 
oratory collaboration  and  commercial  significance  is 
.given  in  language  readily  understood  by  the  average 
man,  yet  not  lacking  in  scientific  information,  by  Tol- 
man1  in  his  article  on  "Secondary  Sulfide  Enrichment 
of  Ores".  Here  is  quoted  his  brief  defini- 
tion of  this  doivmvard  process.  "Secondary  sulfide 
enrichment  involves  three  processes  :  ( 1 )  The  oxida- 
tion of  the  metallic  sulfides;  (2)  The  solution  of  these 
chiefly  as  sulfates,  chlorides  or  bicarbonates ;  and 
(3)  The  precipitation  of  the  metals  in  solution  in  the 
form  of  secondary  sulfides,  (a)  by  the  reduction  of  the 
sulfates  to  metallic  sulfides  by  carbonaceous  matter,  or 

(b)  by  precipitation  by  means  of  hydrogen  sulfide.  or 

(c)  by  reaction  of  the  metallic  salts  with  unoxidized 


I — W.    H.    Emmons,    "The    enrichment    of   sulflde    ores",    Bull. 
U.  S.  G.  S.  No.   529,  p.   11. 


No.  2,  1914)      Clark— Chemistry  of  Cofter  Ore  Enrichment  gl 

sulfides  below  the  water  level,  the  latter  going  into  solu- 
tion as  sulfates,  (or  other  salts),  and  the  former  pre- 
cipitating as  sulfides.  In  the  broadest  sense  secondary 
sulficle  enrichment  includes  deposits  of  any  sulfide  pre- 
cipitated in  any  way  out  of  the  descending  meteoric 
waters  which  owe  their  metallic  content  to  the  leaching 
of  the  overlying  rock." 

A.  F.  Rogers11  has  recently  applied  the  term  upward 
secondary  enrichment  to  processes  by  which  metal- 
bearing  solutions  bring  their  metals  as  sulfides  from 
greater,  and  deposits  them  at  lesser  depths,  in  distinc- 
tion from  processes  in  which  the  oreTforming  solutions 
flow  downward. 

It  is  believed  that  the  results  of  the  present  investi- 
gation have  shown  that  upward  enrichment  without 
oxidation  is  a  very  important  process.  As  will  be  dem- 
onstrated, crystalline  copper  sulfides,  whether  in  the 
form  of  chalcopyrite,  bornite,  covellite  or  chalcocite, 
may  be  brought  into  such  condition  as  to  migrate  con- 
siderable .distances  without  the  intervention  of  any 
process  of  oxidation  or  any  process  converting  the  cop- 
per into  electrolyte  solution.  Such  agencies,  as  will  be 
shown,  are  those  producing  the  colloidal  copper  sul- 
fides. 


I — C.  F.  Tolman,  Jr.,  Min.  and  Sci.  Press.   106,  p.   38,  p.   147, 

p.    178,    (1913). 
H_A.  F.  Rogers,  Econ.  Geol.  8,  p.  781,   (1913). 


§2  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

OXIDATION  AND  SOLUTION  OF  COPPER 
MINERALS. 

A  review  of  the  literature  concerning  these  steps 
shows  that  they  may  take  place  in  one  or  more  of  the 
following  ways : 

( 1 )  Oxidation  of  pyrite  to  produce  sulfuric  acid  and 
ferric  sulfate,  which  then  attack  and  dissolve  chalcocite 
or  other  copper  minerals. 

(2)'  Thru  the  greater  electrolytic  solution  tension  of 
some  minerals  in  contact  with  others. 

(3)  Solution  of  a  mineral  in  pure  water. 

These  three  are  prominently  mentioned  and  are  gen- 
erally accepted  as  being  effective.  To  these  may  be 
added,  as  is  later  shown  by  the  author : 

(4)  Solution  or  dispersion  of  the  mineral  by  car- 
bonated water,  and  that  suggested  but  hardly  proved 
method : 

(5)  Solution  of  the  metal  as  a  chloride  where  pyrite 
and  manganese  dioxide  have  a  chloride  bearing  water 
percolating  thru  them. 

In  addition  to  the  processes  which  have  been  sug- 
gested in'  the  literature  it  will  be  shown  in  this  paper 
that,  (from  the  chemical  point  of  view  at  least),  the 
enrichment  by  the  highly  dispersed  copper  sulfides,  as 
such,  may  be,  as  a  result  of  this  work,  looked  upon  as 
an  important  factor  in  the  general  process  of  enrich- 
ment. 


No.  2,  1914)      Clark— Chemistry  of  Cotfer  Ore  Enrichment  33 

Going  into  detail  concerning  these  methods  of  solu- 
tion we  find  that  the  following  equations  may  represent 
the  oxidation  of  the  pyrite,  though  as  Tolman1  says, 
"the  exact  chemical  equations  are  not  known  and  per- 
haps will  never  be  written"  : 

1.  FeS2  +  4  O  =  FeSO4  +  S 

2.  FeS2  +  6  O  =  FeSO4  +  SO2 

3.  FeS2  +  70  +  H20  =  FeSO4  +  H2SO4 

4.  2  FeSO4  +   H2SO4   +   O  =  Fe2(SO4)3   + 
H2O 

5.  2  Fe2(SO4)3  +  9  H2O  =  2  Fe2O3  .  3H2O  + 
6  H2SO4 

6.  FeS2  +  Fe2(SO4)3  =  3  FeSO4  +  2  S  and 

2  s  +  6  Fe2SO4)3  +  8  H2O  =  12  FeSO4  + 
8  H2S04 

and  according  to  Austin11  the  ferric  sulfate  puts  the 

copper  into  solution  as: 

Fe2(SO4)3  +  Cu2S  =  CuSO4  +  2  FeSO4  +  CuS 
Fe2(SO4)3  +   CuS  +   3  O   +   H2O  =  CuSO4 

+  2  FeS04  +  H2S04 

Buehler  and  Gottschalk111  have  shown  that  chalcocite 

in  contact  with  pyrite  goes  into  solution  as  a  sulfate  in 

the  presence  of  air,  because  of  its  greater  electrolytic 


I— Min.  and  Sci.  Press,  Jan.  4,  18,  and  25,  1913. 
II — Austin,   "The  Metallurgy  of  Common  Metals"  2d  ed..   p. 

281. 

Ill — Buehler  and  Gottschalk,  "The  oxidation  of  sulfldes"  Econ. 
Geol.  5,  pp.  28-37;  7,  pp.  15-35,  1912. 


84  Bulletin  Univertity  of  Mew  Mexico      (Chem.  Ser.  Vol.  I 

solution  tension,  and  that  pyrite,  as  would  be  expected, 
is  little  acted  upon. 

It  may  be  mentioned  in  passing  that  this  is  not  the 
only  possible  explanation  of  this  phenomenon,  which 
may  be  explained  entirely  upon  differences  of  reaction 
velocity  in  the  two  cases.  Of  course  if  definite  equili- 
brium potentials  were  measured  there  would  be  no 
question  as  to  the  validity  of  the  explanation  but  since 
all  copper  sulfide  minerals  show  quite  variable  composi- 
tion it  would  be  natural  to  suppose  that  the  electrolytic 
solution  tensions  would  be  extremely  variable  with  dif- 
ferent specimens.  Until  it  is  possible  to  prepare  chem- 
ically pure  or  nearly  chemically  pure  minerals  of  the 
various  types  any  interpretation  based  upon  the  study 
of  electrolytic  solution  tension  must  be  considered  am- 
biguous. 

Weigel1  has  shown  that  metallic  sul fides  are  slightly 
soluble  in  pure  wrater  without  air. 

Tolman11  was  of  the  opinion  that  copper  minerals 
with  an  excess  of  carbon  dioxide,  in  certain  cases  were 
carried  downward  as  bicarbonates.  The  author  has 
made  such  solutions.  Whether  the  solution  is  a  true 
electrolytic  one  of  copper  bicarbonate  or  a  mere  suspen- 
sion of  a  copper  carbonate  is  an  open  question. 


I — Oscar  Weigel,    "Die   Loslichkeit  von   Schwermetalle   Sul- 
fide   in    reinem   Wasser",    Zeit.    phys.    Chemie,    58,    pp. 
293-300,    (1907). 
II — Suggested  in  Min.  and  Sci.  Press.  Jan.  4,  18,  25,  1913. 


No.  2,  1914)      CJark— Chemistry  of  Co^er  Ore  Enrichmtnt  8£ 

Lane111  believes  that  the  copper  in  the  Michigan 
mines  has  been  carried  downward  as  chloride  solutions 
and  suggests  electrolytic  migration.  That  the  copper 
may  have  been  in  the  chloride  form  seems  wholly  ten- 
able judging  from  the  chloride  content  of  the  Michigan 
mine  waters. 

L,indgrenIV  in  summarizing  Emmon's  work  mentions 
the  possibility  of  solution  as  chlorides  where  nascent 
chlorine  has  played  an  important  role,  this  chlorine 
having  been  produced  in  accordance  with  the  question : 

MnO2  +  4  HC1  =  MnCl2  +  H2O 
He  gives  instances  of  increased  solution  of  gold  when 
manganese  dioxide  has  been  added  to  a  solution  con- 
taining very  dilute  hydrochloric  acid. 

The  above  five  methods  of  oxidation  seem  to  cover 
the  principles  involved.  One  will  find,  however,  men- 
tion of  many  possibilities  of  oxidation  and  solution 
which  combine  two  or  more  of  the  above  methods. 
Considerable  work  has  been  done  in  attempting  to  dis- 
cover the  order  in  which  different  minerals  oxidize.  No 
two  investigators  have  succeeded  in  getting  the  same 
results1.  In  all  the  investigations  made  the  invesigators 
have  failed  to  consider  conditions  under  which  the 
oxidations  took  place  and  their  results  put  the  chemist 


III — A.   C.   Lane,   Mich.  Geol.  and  Biol.   Survey.    Pub.    6,   Geol. 

Ser.    4,   Vol.   I,   p.    43. 

IV — Lindgren,  "Mineral  Deposits,"  p.  798,  1913. 
I — Lindgren,   "Mineral  Deposits,"  p.   787,    1913. 


gg  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

in  mind  of  the  old  Geoffroy  and  Bergmann  affinity 
tables. 

The  essential  factors  entering  into  the  problem  of 
oxidation  are;  ore,  metal,  country  rock,  fissuring, 
porosity,  climate,  water  level,  rainfall,  topography, 
geological  age  and  history  of  the  deposit.  These  have 
to  be  considered  in  the  examination  of  any  particular 
mine. 

PRECIPITATION  OF  THE  METALLIC  SULFIDES. 

Various  methods  have  been  sugested  by  which  the 
metals  in  descending  solutions  of  metallic  salts  can  be 
precipitated  as  sulfides.  The  following  tried  and  un- 
tried means  seem  to  cover  the  possibilities  of  such  pre- 
cipitations : 

( 1 )  Substitution  because  of  solution  tension  of  some 
mineral  precipitant  as ; 

Ag2SO4  +  ZnS  =  Ag2S  +  ZnSO4 
14  CuSO4  +  5  FeS2  +  12  EUO  =  7  Cu2  S  + 
5  FeS04  +  12  H2S04 

(2)  Substitution  in  the  presence  of  sulfur  dioxide 
or  other  reducing  agent  as ; 

4  CuSO4  +  FeS2  +  SO2  +  6  H2O  =  2  Cu2S 
+  FeSO4  +  6  H2SO4. 

(3)  Precipitation  by  means  of  hydrogen  sulfide 

(4)  Precipitation  by  means  of  free  sulfur 

(5)  Neutralization  of  descending  acidic  solutions 

(6)  Precipitation  by  means  of  carbon 


No.  2,1914)      Clark— Chemistry  of  Cofatr  Ore  Enrichment  g7 

(7)   Precipitation  thru  loss  of  a  dispersing  agent1. 

This  paper  has  much  to  do  with  the  last  feature. 

Under  the  first  heading  should  be  noted  the  work  of 
Schuermann11.  He  established  a  series  of  salts  in 
which  the  sulfides  of  any  one  of  the  metals  thereof  will 
be  precipitated  at  the  expense  of  any  sulfide  lower  in 
the  series.  The  series  is  undoubtedly  correct  for  the 
particular  specimens  used  under  the  conditions  which 
his  experiments  were  performed.  What  such  an  order 
might  be  under  other  conditions  one  cannot  say. 

The  work  of  Palmer  and  Bastin1  shows  that  such 
substitution  occurs,  the  author  assumes  because  of  so- 
lution tension.  They  used  many  minerals  and  found 
them  to  precipitate  gold  and  silver.  Two  of  their 
equations  are  here  given; 

2  NiAs  +  5  Ag2SO4  +  3  H2O  =  2  NiSO4  + 

As2O3  +  3  H2SO4  +  10  Ag 
Cu2S  -f  2  Ag2SO4  =  2  CuSO4  +  Ag2S  -f 
2  Ag 

The  first  fact  to  be  considered  under  the  heading  of 
substitution  in  the  presence  of  sulfur  dioxide  or  other 
reducing  agent  is  that  mine  waters  contain  less  and  less 


I — Suggestion  as  to  the  role  of  colloids  is  given  by  P.  Krusch, 
"Primary  and  secondary  ores  considered  with  especial 
reference  to  the  gel  and  the  rich  heavy  metal  ores", 
Min.  and  Sci.   Press,   107,  pp.   418-423,   1913. 
II — Ernst     Schuermann,      "Ueber      die      Verwandschaft      der 
Schwermetalle  zum  Schwefel",  Liebig's  Ann.  d.  Chem. 
249,  p.   326. 
I — Palmer  and  Bastin,  Econ.  Geol.  8,  No.  2,  p.  140,  1913. 


gg  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

oxygen  as  the  depth  increases  as  was  shown  by  Lep- 
sius11.  Emmons111  states  that  the  oxygen  content  and 
acidity  of  descending  waters  diminishes  as  the  depth 
increases.  This  is  strongly  emphasized  in  his  discus- 
sion of  analyses  of  mine  waters. 

Both  TolmanIV  and  WinchelF,  (see  also  experi-. 
ments  No.  9  and  No.  10  in  this  paper),  have  produced 
chalcocite  films  on  pyrite  from  slightly  acid  solutions 
of  copper  sulfate  in  the  presence  of  sulfur  dioxide. 
Chalcocite  was  not  precipitated  in  its  absence. 

W.  H.  EmmonsVI  suggests  that  this  may  be  ex- 
plained by  the  fact  that  sulfur  dioxide  removes  any  at- 
mospheric oxygen  from  the  solutions.  The  author  will 
have  another  conclusion  to  add  to  this. 

All  investigators  are  firm  in  the  belief  that  chalco- 
cite is  not  precipitated  in  the  presence  of  oxidizing 
action. 

In  working  up  their  first  paper  above  mentioned, 
Buehler  and  Gottschalk  obtained  sulfur  dioxide  where 
the  supply  of  oxygen  was  limited. 

Consideration  of  the  next  method,  that  of  precipita- 


II — B.  Lepsius,  "Ueber  die  Abnahme  der  gelosten  Sauer- 
stoffs  in  Grundwasser  and  einen  einfachen  Apparat 
zur  Entahme  von  Tiefproben  in  Bohrochern",  Ber. 
Deut.  Chem.  Ges.  18,  pp.  2487-2490,  1885. 

Ill — Bull.  U.  S.   G.  S.  No.   529,   p.   90. 

IV — Min.  and  Sci.  Press,  106,  p.   38,  p.  141,  p.  178,   1913. 
V — H.  V.  Winchell,   "Synthesis  of  chalcocite  and  its  genesis 
at  Butte,  Mont.   Bull.   Geol.  Soc.  Am.    14,  pp.   272-275. 

VI — Bull.  U.  S.  G.  S.,  No.  529,  p.   52. 


No.  2,  1914)      Clark— Chemistry  of  Cofatr  Or*  Enrichment  §9 

tion  by  means  of  hydrogen  sulfide  formerly  raised  the 
question  as  to  whether  hydrogen  sulfide  can  form  in 
the  zone  of  precipitation.  The  writer  having  estab- 
lished this  fact  that  hydrogen  sulfide  can  form,  refer- 
ences to  data  on  this  point  are  omitted. 

C.  F.  Tolman,  Jr.,  and  A.  F.  Rogers  hold  the  opinion 
that  many  of  our  secondary  copper  deposits  are  in  con- 
tact with  primary  ones  and  that  the  latter  were  brought 
up  by  alkaline  solutions  rich  in  carbon  dioxide  and 
hydrogen  sulfide  and  that  the  escape  or  chemical  as- 
similation of  hydrogen  sulfide  has  disturbed  equili- 
bria sufficiently  to  allow  the  precipitation  of  chalco- 
cite  from  alkaline  solution.  The  writer  has  shown  that 
such  action  is  possible  and  has  shown  the  importance 
of  hydrogen  sulfide  as  a  dispersing  agent. 

Cooke1  was  successful  in  precipitating  silver  sulfide 
by  means  of  amorphous  sulfur.  Vogt11  and  Stokes111 
have  shown  that  amorphous  sulfur  can  readily  form  in 
nature. 

One  of  the  writer's  most  important  conclusions  deals 
with  this  action  of  amorphous  sulfur. 

Data    on    precipitation    thru    neutralization    of    de- 


I — H.  C.  Cooke,  "The  secondary  enrichment  of  silver  ores", 

Jour.   Geol.   21,   No.   1,   p.    1. 
II — J.   H.   L,.  Vogt,   "Problems  in   geology  of  ore  deposits,"   in 

Posepny,   Franz.      "The  Genesis  of  Ore  Deposits,"  pp. 

676-677,    1902. 
Ill — H.  N.  Stokes,  Econ.  Geol.  2,  pp.   14-23,   1907. 


90  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

scending  acidic  solutions  are  rather  numerous.  E.  C. 
Sullivan1  secured  a  loss  in  copper  content  of  such  solu- 
tions by  absorption  or  neutralization  by  keeping  them  in 
contact  with  powdered  orthoclase  albite,  amphibole, 
shale,  and  clay  gouge.  Grout11  has  secured  precipita- 
tion by  neutralization  with  rather  strong  alkalies.  His 
work  is  largely  qualitative.  W.  H.  Emmons111  makes 
reference  to  the  work  of  Ransome,  Kemp  and  Lind- 
gren,  who  show  how  limestone  can  be  attacked  by  de- 
scending acid  waters  and  can  precipitate  malachite  and 
azurite  in  accordance  with  these  equations : 

2  CuSO4  +  2  CaCO3  -f  5  H2O  =  CuCO3.Cu 
(OH)2  +  2  CaSO4  +  2  H2O  +  CO2 

2  CuS04  -f  3  CaC03  +  7  H,O  =  2  CuCOa.Cu 
(OH)2  +  3  CaSO4  +  2  H2O  -f  CO2 

The  writer  has  secured  some  data  on  this  subject  of 
neutralization  and  its  effect  on  precipitation. 

Finally  Lindgren,  Graton  and  GordonIV  show  chal- 
cocite  in  coal,  and  give  reduction  by  carbon  as  the  cause 
of  its  deposition.  Their  equation  is 

4  CuSO4  +  5  C  +  2  H2O  =  Cu2S  +  H2SO4  + 
5  C02 


I — E.  C.  Sullivan,  "The  interaction  between  minerals  and 
water  solutions,  with  special  reference  to  geologic 
phenomena".  Bull.  U.  S.  G.  S.  No.  312,  pp.  37-64, 
1907. 

II — Econ.   Geol.  8,   p.   407-433,   Aug.    1913. 
Ill — Bull.  U.  S.   G.   S.  No.   529,  p.   101. 


No.  2,1914)      Clark— Chemistry  of  Coffer  Ore  Enrichment  91 

Reference  and  detail  of  work  done  are  given  under  the 
writer's  experiment  No.  25. 

CHEMICAL  OUTLINE  OF  THIS  INVESTIGATION 

AND  REFERENCE  TO  GEOLOGICAL 

APPLICATIONS. 

The  results  of  this  research,  from  the  point  of  view 
of  the  chemist,  may  be  considered  as  having  to  deal 
with  two  classes  of  metal-bearing  solutions,  (A)  Solu- 
tions in  which  the  copper  is  in  the  form  of  an  electro- 
lyte, and  (B)  Solutions  of  colloidal  copper  sulfides. 

Taking  up  the  matter  covered  by  the  first  heading 
we  come  at  once  to  oxidation.  This  was  investi- 
gated early  in  the  work.  Failure  to  secure  the  solution  of 
copper  asasulfateinmore  than  traces,  thru  the  agency 
of  dissolved  oxygen,  (see  exp.  No.  1,  No.  2,  No.  3, 
No.  4  and  No.  6)  and  great  success  in  securing  such 
when  alternate  drying  and  moistening  were  resorted  to, 
(experiment  No.  5),  fully  confirmed  the  views  of 
Spencer1  that  dissolved  oxygen  probably  cannot  pro- 
duce enough  copper  sulfate  to  form  deposits  of  any  con- 
sequence, and  that  in  the  zone  of  leaching  we  must  have 
sufficient  porosity  to  admit  atmospheric  air.  The  con- 
ditions under  which  the  writer  secured  strong  oxidation 
are  those  of  the  mining  districts  of  the  Southwest, 
where  torrential  rainfall  is  followed  by  long  period 
of  drought. 


I — Econ.  Geol.  8,  p.   631. 


92  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  1 

This  work  has  shown  that  carbonate  ores  may,  thru 
the  agency  of  carbonated  meteoric  waters,  go  into  solu- 
tion or  suspension  and  thus  may  readily  contribute  to 
the  supply  of  copper  in  descending  waters.  (Experi- 
ments No.  7  and  No.  8.) 

Probably  one  of  the  earliest  recorded  syntheses  of 
chalcocite  is  that  of  Winchell11  and  Tolman.  They 
used  acid  copper  sulfate  solution  with  sulfur  dioxide 
and  secured  a  deposit  on  pyrite.  The  author  has  con- 
firmed this  result  and  has  shown  the  great  importance 
of  impurities  in  the  pyrite,  (Experiment  No.  9),  and 
he  has  also  established  the  fact  that  sulfur  dioxide  plays 
the  role  of  a  strong  reducing  agent,  as  thru  its  use  he 
produced  a  crystalline  cupro-cupric  sulfite,  (Experi- 
ment No.  10).  In  all  solutions  in  which  he  used  sulfur 
dioxide  the  precipitation  of  copper  sulfide  was  greatly 
increased.  (Experiment  No.  20.)  It  is  interesting  to 
note  in  this  connection  that  in  the  presence  of  ferrous 
sulfate,  which  generally  has  been  thought  to  be  an  al- 
most indispensable  agent  for  the  securing  of  chalcocite 
precipitation,  the  chalcocite  is  not  as  readily  precipi- 
tated as  in  the  absence  of  ferrous  sulfate,  but  that  the 
introduction  of  sulfur  dioxide  into  such  solutions  con- 
taining ferrous  sulfate,  greatly  increases  this  deposi- 
tion. (Experiment  No.  20).  Acidity  is  shown  to  be 
less  favorable  than  neutrality  or  alkalinity.  As  will  be 


II — H.  V.  Winchell,  "Synthesis  of  chalcocite,  etc."  Bull.  Geol. 
Soc.   Am.    14,   269-276. 


No.  2,  1914)       CJari— Chemistry  of  Co^er  Ore  Enrichment  93 

shown  hydrogen  sulfide  is  a  powerful  dispersing  agent 
and  is  inimical  to  the  deposition  of  the  sulfides.  Sul- 
fide dioxide  by  its  action  on  hydrogen  sulfide,  2  H2S 
-j-  SO2  =  2  H2O  +  3  S,  tends  to  overcome  this  dis- 
persing action  and  in  this  manner  also  favors  precipi- 
tation. 

Doelter1  is  impressed  with  the  fact  that  practically 
all  substances  are  colloidal  when  first  precipitated,  yet 
that  the  crystalline  condition  seems  to  be  the  stable  one 
in  nature.  He  reviews  the  work  and  ideas  of  others 
and  seems  to  conclude  that  what  we  call  amorphous 
substances  are  very  close  to  the  crystalline.  He  speaks 
of  the  fact  that  the  tendency  to  pass  from  the  colloidal 
to  the  crystalline  condition  is  greatly  increased  by  pres- 
sure, shock,  light  and  influence  of  Rontgen  rays  and 
radium  rays  and  describes  his  own  very  successful  work 
in  producing  crystalline  material  by  means  of  shaking, 
long  continued  heating  and  particularly  by  means  of 
pressure,  and  concludes  that  many  minerals  whose  for- 
mation was  once  thought  to  require  high  temperatures 
may  easily  be  formed  without  such  temperatures.  The 
ideas  brought  out  in  the  paper  seem  particularly  ger- 
mane to  the  deposition  and  formation  of  massive  chal- 
cocite. 


Doelter,  "Ueber  die  Umwandlung  amorpher  Korper  in 
Kristallinische",  Zeit.  f.  Chemie  und  Industrie  der  Kol- 
loide.  Band  8,  heft  1  s  29,  heft  2,  s  86. 


94  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  1 

Thru  shock  the  cupro-cupric  sulfite  crystals  men- 
tioned above  were  produced  by  the  author. 

This  fact  that  all  precipitations  are  first  colloidal  was 
found  to  apply  particularly  to  the  sulfides  of  copper, 
and  we  now  consider  such  colloidal  solutions,  our  sec- 
ond main  (B)  topic  of  investigation.  Under  this  is 
taken  up:  1st,  The  formation  of  colloidal  amorphous 
copper  sulfides;  2d,  The  chemical  conduct  of  amor- 
phous copper  sulfides,  and,  3d,  The  physical  conduct  of 
amorphous  copper  sulfides. 

This  work  shows  clearly  that  colloidal  copper  sul- 
fides can  be  formed  from  sulfate  solutions  and  from 
the  dispersion  of  crystalline  or  massive  sulfides. 

Taking  up  the  formation  of  the  sulfides  from  sulfate 
solution  is  was  found  that  this  could  be  brought  about 
by  any  one  of  four  methods. 

Hydrogen  sulfide,  as  is  well  known,  is  very  effici- 
ent, and  that  it  is  quite  possible  geologically  to  have  this 
hydrogen  sulfide  in  the  earth  was  shown  in  experi- 
ments No.  22  and  No.  23.  Hydrogen  sulfide  was  pro- 
duced by  the  action  of  water  on  pyrite  and  it  was  also 
produced  by  the  action  of  very  dilute  acid  on  pyrite, 
chalcopyrite  and  bornite  the  relative  development  of 
hydrogen  sulfide  decreasing  as  the  iron  content  of  the 
minerals  decreased. 

Amorphous  sulfur  was  found,  to  precipitate  a  sulfide 
of  copper  from  copper  sulfite  solution,  this  action  be- 
ing very  rapid  with  fresh  amorphous  sulfur,  prepared 


No.  2,  1914)      Clark— Chemistry  of  Cofaer  Ore  Enrichment  95 

by  the  action  of  hydrogen  sulfide  on  sulfur  dioxide, 
freed  from  the  gases  and  suspended  in  water,  yet  fall- 
ing off  rapidly  as  the  sulfur  aged.  Experiment  No.  19 
shows  this  action,  the  curve  being  very  striking.  That 
sulfur  should  have  this  action  is  not  at  all  surprising. 
The  equation,  3  S  +  2  H2O  =  2  H2S  +  SO2  is  known 
to  be  reversible.  Stokes'1  work  readily  accounts  for 
the  presence  of  amorphous  sulfur  in  the  zone  of  preci- 
pitation. 

Several  instances  of  production  of  amorphous  cop- 
per sulfides  by  the  action  of  sulfide  minerals,  particu- 
larly pyrite,  on  copper  sulfate  solution  are  shown  in 
experiments  No.  .20,  No.  21,  and  No".  35.  Formerly 
this  was  thought  to  be  the  one  method  of  sulfide 
production. 

Finally,  amorphous  copper  sulfides  were  produced  by 
the  action  of  a  thiosulfate  solution  on  one  of  copper 
sulfate.  This  action  at  first  formed  the  double  thiosul- 
fate of  sodium  and  copper  which  then  decomposed  to 
give  a  mixture  of  amorphous  cupric  and  cuprous  sul- 
fides. Details  of  this  work  and  references  showing 
this  action  to  be  possible  geologically  are  given  ex- 
periments No.  18  and  No.  24. 

By  the  dispersion  of  crystalline  and  massive  sulfides, 
the  colloidal  forms  are  very  readily  produced,  and  most 
effective  for  this  dispersion  is  the  agent  hydrogen  sul- 


I — Econ.  Geol.  2,   14-23,   1907. 


96  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  1 

fide.  This  disperses  the  crystalline  or  massive  material 
in  acid  solution,  (Experiment  No.  43,  No.  26,  No.  27 
and  No.  28),  and  enormously  more  effectively  in  alka- 
line solutions,  (Experiment  No.  44,  No.  38,  No.  39, 
No.  40  and  41).  The  dispersion  increases  in  a  series 
chalcopyrite,  bornite,  covellite  and  chalcocite  as  the 
copper  content  of  the  minerals  increases,  which  indi- 
cates a  strong  tendency  for  the  sulfide  of  copper  to 
migrate  away  from  a  sulfide  of  iron.  Thus  we  see  why 
chalcocite  and  chalcopyrite  are  so  abundant,  the  former 
the  one  to  migrate  most  and  the  latter  to  resist  this 
action  the  longest. 

It  seems  probable  that  the  hydrogen  sulfide  forms  an 
unstable  compound  with  the  copper  sulfide.  Linder 
and  Picton1  have  shown  that  the  dispersed  material  has 
a  slightly  larger  sulfur  content  than  the  undispersed. 

Free  amorphous  sulfur  has  the  effect  of  dispersing 
a  massive  or  crystalline  sulfide.  This  is  very  forcefully 
shown  in  Experiment  No.  13.  In  about  four  months  a 
lump  of  chalcocite  weighing  seven  grams  lost  over  one 
gram  in  weight  when  sealed  in  a  flask  in  contact  with 
this  amorphous  sulfur. 

Now,  coming  to  the  second  part  of  our  main  head- 
ing (B)  we  may  consider  the  chemical  conduct  of 
amorphous  copper  sulfides.  Probably  the  most  im- 


I — Linder  and  Picton,  "Some  physical  properties  of  arsenious 
sulfides  and  other  solutions".  Jour.  Chem.  Soc.,  67, 
p  63,  1895. 


No.  2,  1914)      Clark— Chemistry  of  Co^er  Ore   Enrichment  97 

portant  point  in  this  investigation  is  concerned  with  the 
discovery  of  the  fact  that  at  ordinary  temperatures  cu- 
pric  sulfide  in  contact  with  water  spontaneously  decom- 
poses to  cuprous  sulfide  and  sulfur,  2  CuS  =  Cu2S  + 
S.  (Experiments  No.  31,  No.  12,  No.  15,  No.  17, 
Xo.  18,  No.  24,  No.  26,  No.  27,  No.  29,  No.  30,  and 
No.  33.) 

Fraulein  Wassjuchnowa11  showed  that  this  action 
takes  place  in  the  dry  state  at  temperatures  above  500 
degrees. 

From  the  number  of  experiments  cited  one  can  see 
that  this  transformation  took  place  very  readily.  It  did 
not,  however,  take  place  as  readily  in  the  presence  of 
ferrous  sulfate  as  in  its  absence,  (Ex.  No.  14  and  Ex. 
No.  16),  and  in  those  cases  in  which  a  large  excess  of 
free  sulfur  was  used  no  large  amount  of  Cu2S  was 
obtained  in  the  length  of  time  which  the  material  stood. 
Cu2S  was  also  produced  by  use  of  sodium  arsenite. 
This  is  described  and  discussed  under  experiment 
No.  32. 

Finally  coming  to  the  physical  conduct  of  the  amor- 
phous copper  sulfides  it  is  to  be  noticed  that  there  is  a 
tendency  for  them  to  accrete  on  certain  minerals,  and 
that  they  deposit  from  their  dispersed  condition  when 
those  agents  which  favor  dispersion  have  their  effects 
lessened.  In  experiment  No.  13  it  was  found  that 


II — Zeitschr.  f.   Electrochemie  19,  No.   22,   p   902,   1913. 


98  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

some  sulfide  had  gathered  on  chalcopyrite  and  in  No. 
29  a  heavy  dense  growth  was  noted  on  bornite.  Be- 
cause of  the  relatively  very  much  greater  accretion  on 
the  bornite  it  would  seem  that  this  mineral  may  become 
chalcocite  thru  continued  addition  of  copper  sulfide, 
(See  also  Ex.  No.  42).  The  same  may  be  said  of  chal- 
copyrite tho  in  the  case  of  this  mineral  the  action  would 
be  very  much  slower.  The  fact  that  it  is.  practically  im- 
possible to  find  a  chalcocite  which  is  free  from  specks  of 
bornite  gives  additional  weight  to  this  view.  This 
again  is  checked  by  microscopic  evidence  produced  by 
Tolman  and  Ray1. 

The  author  was  able  to  cause  copper  sulfide  to  ac- 
crete on  sphalerite,  (Ex.  No.  30),  and  also  on  chalco- 
cite as  Cu2S  the  phenomenon  in  this  case  being  caused 
by  the  removal  of  a  dispersing  agent,  H2S. 

The  effect  of  the  removal  of  this  dispering  agent 
H2S  is  well  brought  out  in  Experiment  No.  33.  Here 
both  crystalline,  (apparently),  and  amorphous  sulfides 
were  thrown  down  as  t*\e  hydrogen  sulfide  was  re- 
leased.. Moreover  with  a  reduction  of  alkalinity,  such 
as  in  nature  could  be  accounted  for  by  descending  acidic 
waters  mingling  with  the  alkaline  solutions,  a  precipi- 
tate of  the  amorphous  sulffde  was  produced. 

With  the  complete  elimination  of  hydrogen  sulfide 
as  is  seen  in  experiment  No.  41  and  as  seen  in  tendency 


T — Unpublished   manuscript. 


No.  2 ,  1 9 1 4  )      CJari  -  Chemistry  of  Co^er  Ore  Enrichment  99 

in  experiments  No.  38  and  No.  40,  crystalline  chalco- 
cite  was  produced. 

The  above  discussion  throws  some  light  on  the  ques- 
tion as  to  why  chalcocite  and  chalcopyrite  are  the  chief 
copper  minerals  of  our  mines. 

This  investigation  was  started  with  the  view  of  de- 
termining why  such  should  be  the  case,  and  it  ends 
apparently  with  finding  no  reason  why  such  should  not 
be  the  case.  All  the  processes  involved  in  enrichment 
tend  toward  the  formation  of  chalcocite.  Only  under 
particular  conditions,  (absence  of  hydrogen  sulfide  or 
presence  of  sulfur  dioxide),  would  this  be  crystalline. 

It  is  nevertheless  evident  that  chalcocite,  either  crys- 
talline or  amorphous  is  the  ultimate  stable  form  toward 
which  all  copper-bearing  minerals  tend  when  in  contact 
with  solution.  All  other  copper  sulfide  minerals  are 
to  be  looked  on  as  unstable.  Of  these  chalcopyrite 
shows  in  all  reactions  a  very  low  reaction  rate  which 
accounts  for  its  apparently  greater  stability. 

PREFACE  TO  EXPERIMENTS. 

From  the  beginning  of  the  work  the  author  acted  on 
no  preconceived  opinions  but  attempted  to  get  data  on 
any  phase  of  the  subject  by  means  of  any  experiment 
which  seemed  to  have  a  fair  chance  of  being  productive, 
and  in  all  over  sixty  experiments  were  tried. 

Each  experiment  was  carried  on  carefully  but  with 


100  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

attention  to  exactness  commensurate  with  the  expected 
results.  This  may  be  illustrated  by  the  statement  that 
the  cyanide  method  was  used  in  determining  copper  in 
some  experiments,  while  in  others  gravimetric  deter- 
minations were  made  on  a  very  sensitive  button  balance, 
and  all  regeants  were  made  up  of  selected  crystals  from 
C.  P.  analysed  chemicals. 

Duplication  of  the  work  will  undoubtedly  give  closer 
figures  at  some  points.  It  probably  will  alter  no  prin- 
ciple established  here  from  experimental  basis. 

All  experiments  were  carried  on  in  the  light  and  at 
ordinary  laboratory  temperature  except  as  otherwise 
stated. 

Experiment  No.  i. — Study  of  oxidation  of  pyrite  and 

of  a  pyrite  and  chalcocite  mixture. 

In  belief  that  more  light  could  be  thrown  on  the  sub- 
ject of  oxidation  of  pyrite  and  of  pyrite  and  chalcocite 
mixtures,  if  such  were  in  the  form  of  very  finely  di- 
vided material  which  would  be  kept  in  water,  this  water 
being  always  saturated  with  oxygen,  100  grams  of  very 
pure  pyrite  which  had  been  put  thru  a  200-mesh  sieve 
were  put  into  a  long,  narrow  separatory  funnel  and 
covered  with  water.  A  tube  was  led  into  this  and 
every  third  day  oxygen  was  allowed  to  bubble  thru  the 
water  for  24  hours. 

At  the  end  of  the  first  12  hours  evidence  of  oxidation 
was  seen.  This  continued  to  increase.  Ferrous  sulfate 
gathered  in  solution  at  the  bottom  of  the  cylinder  and 
an  "iron  hat"  formed  at  the  top.  This  oxidation  did 
not  go  on  as  fast  as  it  had  been  expected  to,  and  in  view 
of  other  data  obtained,  (see  Experiment  No.  5),  the 


No.  2,  1914)      Clark— Chemistry  of  Coffer  Ore  Enrichment  \Ql 

passage  of  oxygen  was  discontinued,  and  the  liquid  was 
allowed  to  pass  thru  the  pyrite  and  drain  into  a  recep- 
tacle once  each  day.  The  drainings  were  poured  back 
into  the  cylinder  daily.  This  treatment  increased  the 
oxidation.  At  the  end  of  5  months  the  liquid  contained 
0.0393  g  SO4  and  0.0147  g  H2SO4.  The  balance  of 
the  sulfate  radical  was  distributed  between  ferrous  and 
ferric  iron. 

A  mixture  of  50  grams  200  mesh  pyrite  and  200 
mesh  chalcocite1  \vhich  had  been  treated  in  the  same 
way,  except  for  the  passage  of  oxygen  gave  at  the  end 
of  5^  months  a  solution  which  contained  merely  a 
trace  of  copper. 

In  view  of  the  large  amount  of  copper  obtained  by 
Buehler  and  Gottschalk11,  the  idea  suggested  itself  that 
as  the  cylinder  was  very  long  a  precipitation  of  the 
copper  sulfide  might  have  taken  place  in  the  lower  part 
of  this  cylinder.  This  was  not  investigated. 
Experiment  No.  2. — Study  of  oxidation  in  the  presence 

of  pyrite,  manganese  dioxide  and  solution  of  sodium 

chloride. 

With  the  view  of  securing  some  data  on  the  idea 
suggested  by  Lane111,  that  copper  minerals  may  go  into 
solution  in  the  form  of  chlorides,  50  grams  of  200 
mesh  pyrite,  50  grams  200  mesh  chalcocite  and  0.5 
gram  200  mesh  manganese  dioxide  were  put  into  a 
long,  narrow  separatory  cylinder,  covered  with  N/20 


I — A  very  fine,  exceedingly  pure  specimen  furnished  by  Mr. 
A.  C.  Duhrs  of  Butte,  Mont.     Polished  sections  showed 
only  mere  traces  of  bornite. 
II — Buehler    and    Gottschalk.    "The    Oxidation    of    sulfides" 

Econ.  Geol.  5,  pp  28-35;    7,  pp   15-35. 

Ill — A.  C.  Lane,   Mich.   Geol.  and  Biol.  Survey.   Pub.   6,  Geol. 
Series   4,   Vol.    2. 


1Q2  Bulletin  Univertity  ofN.ew  Mexico      (Chem.  Ser.  Vol.  I 

NaCl  and  treated  with  oxygen,  etc.,  exactly  as  in  Ex- 
periment No.  1. 

At  the  end  of  5*/2  months  only  a  trace  of  copper  had 
gone  into  solution,  tho  much  manganese  had  gone  into 
solution  and  had  redeposited,  evidently  as  hydrated 
oxide. 

Experiment  No.  j. — Study  of  solution  of  chalcocitc. 

A  mixture  of  chalcocite  and  pyrite  was  treated  as 
described  in  experiment  No.  1.  The  water  was  kept 
saturated  with  oxygen  for  two  months  and  then  for 
3J/2  months  the  tube  was  drained  daily.  Merely  a  trace 
of  copper  was  found  in  solution. 

Experiment  No.  4. — I Attempt  to  secure  copper  in  solu- 
tion as  a  bicarbonate. 

In  the  belief  that  oxidation  would  be  very  rapid  if 
the  minerals  were  very  finely  divided  and  if  they  were 
kept  in  water  saturated  with  oxygen,  50  grams  200  mesh 
chalcocite,  50  grams  200  mesh  pyrite  and  50  grams  of 
60  mesh  marble  were  put  into  a  separatory  funnel  and 
treated  as  described  in  Experiment  Xo.  1.  Evidently 
the  marble  immediately  used  up  any  trace  of  sulfuric 
acid  that  was  formed  as  no  copper  went  into  solution. 

Experiment  No.  5. — Study  of  oxidation  of  chalcocite. 

Spencer11  suggests  that  oxidation  is  most  rapid 
where  the  ore  is  merely  kept  moist,  and  shows  theoretic- 
ally, at  least,  how  the  oxidation  requires  more  oxygen 
than  can  be  obtained  from  water  solution. 

Two  glass  tubes  12"  x  2"  were  nearly  sealed  at  each 
end.  Thru  the  holes  left  open  10  grams  of  200  mesh 
chalcocite  was  introduced  into  one,  and  10  grams  of 

I — Tolman,  "Secondary  sulfide  enrichment  of  ores"  Min.  and 

.  Sci.  Press.     106,  p  180,   1913. 
II — Spencer,  Econ.  Geol.  8,  p  631. 


No.  2,  1914)      Clark— Chemistry  of  Cofatr  Ore  Enrichment  1Q3 

200  mesh  chalcocite  with  10  grams  200  mesh  pyrite 
was  put  into  the  other.  The  mineral  was  covered  with 
water  and  the  tubes  were  set  aside.  These  tubes  were 
revolved  once  each  day,  thus  the  mineral  was  alter- 
nately moistened  and  dried. 

At  the  end  of  only  29  days  the  liquid  from  the  first 
tube  showed  a  strong  trace  of  copper.  The  liquid  from 
the  second  tube  showed  0.01896  g  copper  in  solution. 

Experiment  No.  6. — Attempt  to  secure  oxidation  data. 

In  the  belief  that  oxygen  which  could  be  liberated 
from  hydrogen  peroxide,  would  be  liberated  rather 
evenly  thruout  a  mixture  of  powdered  chalcocite  and 
pyrite  thus  rapidly  producing  copper  sulfate,  a  separa- 
tory  funnel  was  prepared  as  described  under  experi- 
ment No.  1.  The  minerals  acted  as  catalysers  for  the 
decomposition  of  the  hydrogen  peroxide,  and  at  the 
end  of  a  day  or  two  about  all  the  available  oxygen  had 
been  set  free.  No  trace  of  copper  sulfate  was  secured. 
Experiment  No.  7. — Study  of  solution  of  malachite, 

azuritc  and  chrysacolla. 

As  a  result  of  mnny  obcervations  made  in  and  around 
mines  Professor  C.  F.  Tolman,  Jr.,  is  of  the  opinion 
that  these  minerals  can  migrate  downward,  probably  as 
bicarbonates. 

Twelve  gas  washing  bottles  were  taken.  To  each  of 
3  was  added  30  cc  N/2  potassium  carbonate,  to  each 
of  3  others  30  cc  potassium  carbonate  with  a  little  so- 
dium silicate,  to  each  of  3  others  30  cc  dilute  sodium  sili- 
cate solution,  and  to  each  of  3  others  30  cc  of  water,  thus 
making  3  sets  of  4  liquids  in  each  set.  I  gram  200 
mesh  malachite  was  added  to  each  bottle  in  one  set,  1 
gram  200  mesh  azurite  to  each  bottle  in  the  second  set 
and  1  gram  200  mesh  chrysacolla  to  each  in  the  third. 

Carbon  dioxide  was  passed  thru  each  bottle  for  one 


J(J^.  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

month.    At  the  end  of  this  time  it  was  found  that  there 
was  a  trace  of  copper  in  the  solution  in  each  bottle,  the 
liquids  coming  from  the  bottles  containing  chrysacolla 
and  water,  azurite  and  N/2  potassium  carbonate  and 
azurite  and  water  giving  the  strongest  tests. 
Experiment  No.  8. — Amount  'of  copper  going  into  so- 
lution or  suspension  from  azurite  and  from  chrysa- 
colla. 

To  a  gas  washing  bottle  "was  added  1  gram  200  mesh 
chrysacolla  and  100  cc  water,  to  a  second  1  gram  200 
mesh  azurite  and  100  cc  water  and  to  a  third  1  gram 
200  mesh  azurite  and  100  cc  N/2  potassium  carbonate. 
Carbon  dioxide  was  passed  thru  each  bottle  very 
slowly  for  96  days.  The  liquid  in  the  first  bottle  was 
filtered  and  analysed.  It  contained  0.0004  g  copper. 
The  liquid  in  the  second  contained  0.0007  g  copper  and 
the  liquid  in  the  third  0.0007  g. 

Experiment  No.  p. — Synthesis  of  chalcocite.      (Win- 
chell-Tolman1  experiment). 

The  experiment  as  described  by  these  authors  was 
repeated. 

A  lump  of  exceedingly  pure  pyrite  was  taken  and 
placed  into  a  solution  of  copper  sulfate  (1  cc  = 
0.019665  g  Cu)  whose  acidity  with  sulfuric  acid  was 
X/20.  This  was  then  saturated  with  SO2  and  the 
whole  was  sealed  in  a  bottle. 

At  the  end  of  18  days  a  faint  trace  of  dark  material 
appeared  on  some  of  the  surfaces  of  the  pyrite.  At  the 
end  of  one  month  one  end  of  the  pyrite  was  strongly 
coated  while  the  other  was  as  bright  as  ever.  At  the 
end  of  5  months  a  uniform  black  coating  covered  the 
pyrite. 


I — H.   V.   Winchell,   "Synthesis   of  chalcocite   etc"   Bull.   Geol. 
Soc.  Am.  14,  269-276. 


No.  2,  1914)       Clark— Chemistry  of  Cofaer  Ore  Enrichment  1(J5 

Experiment  No.  10. — Attempted  synthesis  of  chalco- 

clte.     (Winchell-Tolman  experiment  modified). 

Because  the  tarnishing  of  the  pyrite  was  so  long  de- 
layed in  Experiment  No.  9  it  was  believed  that  impuri- 
ties were  necessary  for  the  formation  of  chalcocite,  and 
as  the  analysis  of  the  pyrite  used  by  Winchell  and  Tol- 
man  showed  the  presence  of  zinc,  a  crystal  of  sphalerite 
was  wired  to  a  piece  of  very  pure  pyrite  with  platinum 
wire.  This  couple  was  then  put  into  a  solution  such  as 
was  used  in  No.  9  and  the  flask  was  sealed. 

At  the  end  of  46  days  no  marked  change  could  be 
seen.  On  the  47th  day  the  flask  was  accidentally  sub- 
jected to  great  jarring  and  on  the  48th  day  small  ruby 
red  crystals  were  seen.  These  were  prismatic,  had 
high  relief,  were  pleochroic  and  had  parallel  extinction. 

As  they  gave  all  the  tests  for  cupro-cupric  sulfite  as 
described  by  Segerbloom  in  his  ''Table  of  Properties" 
they  were  undoubtedly  cupro-cupric  sulfite. 

This  experiment  confirms  the  belief  of  Winchell1 
and  Spencer11  that  SO2  plays  the  role  of  a  strong  reduc- 
ing agent.  It  also  tends  to  confirm  the  opinion  of 
Lindgren111  that  pyrite  does  not  precipitate  Cu2S  or 
CuS  while  zinc  blende  is  present.  Neither  sulfide 
formed  after  months  of  standing. 

Experiment  No.   n. — Effect  of  jarring  on  crystalla- 

tion. 

The  experiment  as  described  under  No.  10  was  re- 
peated. The  sealed  bottle  was  allowed  to  stand  for 
nearly  double  the  length  of  time  which  the  bottle  stood 
in  No.  10.  No  crystals  appeared.  The  bottle  was  then 


I — Bull.  Geol.  Soc.  Am.   14,  pp   273-275. 
II — A.  C.  Spencer,  "Chalcocite  deposition"  Jour.  Wash.  Acad. 

Sci.  3,  pp  70-75,   1913. 
Ill — Lindgren  etc.  Prof.  Paper.  U.  S.  G.  S.  No.  43,  p  183,  1905. 


10(3  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

subjected  to  considerable  jarring  and  crystals  appeared 

within  a  few  hours. 

Experiment  No.  12. — Production  of  cuprous  sulfide. 

H2S  was  passed  thru  a  solution  of  CuSO4  until  all 
of  the  copper  had  precipitated  as  CuS.  The  liquid  was 
filtered  off  and  the  precipitate  was  surrounded  with 
H2S  water,  and  sealed  in  a  flask  with  an  atmosphere  of 
H2S. 

At  the  end  of  24  hours  a  ring  of  what  was,  from  its 
color,  covellite  streaked  the  flask  at  the  surface  of  the 
precipitate.  At  the  end  of  a  few  days  this  covellite  was 
not  noticeable. 

The  flask  was  opened  at  the  end  of  130  days.  The 
residue  showed  an  abundant  separation  of  sulfur  when 
examined  with  the  microscope. 

This  residue  was  washed,  dried,  extracted  with  CS2 
and  0.7173  g  was  taken  for  analysis.  This  gave 
0.1723  g  sulfur  thus  leaving  0.5450  g  copper. 

0.7173  g  Cu2S  contains  0.5729  g  Cu. 

0.7173  g  CuS  contains  0.4767  g  Cu. 

On  the  basis  of  the  copper  content  this  residue  con- 
tained 70.99%  Cu2S. 

Experiment  No.  75. — To  observe  transference,  substi- 
tution or  growth. 

A  lump  of  chalcocite  weighing  7.6332  g  and  a  lump 
of  chalcopyrite  weighing  3.2458  g  were  sealed  in  a 
flask  with  50  cc  copper  sulfate  solution,  ( 1  cc  =• 
0.039331  g  Cu),  50  cc  ferrous  sulfate  solution,  (1  cc  = 
0.026243  g  Fe) ,  and  a  large  excess  of  amorphous  sulfur, 
(2  days  old)  and  an  atmosphere  of  carbon  dioxide. 

A  decided  growth  of  black  material  was  observed  on 
and  in  contact  with  the  chalcocite  at  the  end  of  two 
weeks. 

The  flask  was  opened  at  the  end  of  137  days.     The 


No.  2,  1914)      Clark— Chemistry  of  Cofar  Ore  Enrichment  1Q7 

chalcocite  lump  remained  attached  to  the  bottom  of  the 
flask.  This  lump  was  covered  with  a  black  velvety 
film  which  stood  out  in  ridges  on  the  lump.  The  film, 
(very  loosely  attached),  was  removed  and  the  lump 
was  weighed.  It  weighed  6.5745  g — a  loss  of  1.0587  g. 

This  film  and  the  general  residue  in  the  flask  were 
analysed.  Both  contained  iron  which  made  exact  re- 
sults as  to  Cu2S  and  to  CuS  of  little  value.  The  fact 
that  the  film  had  a  copper  content  of  69.03%  Cu,  while 
the  general  residue  contained  64.73%  showed  the 
greater  copper  content  to  be  nearer  the  lump  of  chal- 
cocite. 

It  seems  probable  that  in  the  presence  of  the  excess 
of  amorphous  sulfur  that  the  sulfide  was  mostly  CuS 
tho  some  Cu2S  was  probably  present  in  the  film. 

The  chalcopyrite  lump  was  loose  and  came  out  of  the 
flask  readily.  It  weighed  3.2473  g — a  gain  of  0.0015 
g.  A  deposit  of  black  sulfide  hung  tenaceously  to  the 
lump  and  could  not  be  washed  off.  This  would  account 
for  the  gain,  and  would  indicate  that  chalcocite  can 
grow  on  or  at  the  expense  of  chalcopyrite,  but  not  as 
readily  as  on  or  at  the  expense  of  bornite.  (See  Ex- 
periment No.  29). 

This  experiment  was  repeated  with  amorphous  sul- 
fur which  was  one  day  old,  and  similar  results  were  ob- 
tained. It  was  also  repeated  with  freshly  prepared 
amorphous  sulfur.  The  final  results  were  much  as 
given  above. 

Experiment  No.  14. — To  observe  transference,  substi- 
tution or  growth. 

As  described  under  No.  13,  a  lump  of  chalcocite  and 
a  lump  of  chalcopyrite  were  put  into  a  solution  of  cop- 
per sulfate  mixed  with  one  of  ferrous  sulfate  and  sealed 
in  an  atmosphere  of  CO2. 


108  BuUetin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

At  the  end  of  76  days  the  chalcocite  showed  a  loss  of 
0.0817  g.  The  weight  of  the  chalcopyrite  was  un- 
changed. 

This  agrees  with  the  results  obtained  by  Emmons 
and  Groutiv.    They  secured  no  chalcocite  deposition  by 
using  ferrous  sulfate  as  a  reducing  agent. 
Experiment  No.  15. — Production  of  cuprous  sulfide. 

Cupric  sulfide  was  washed  free  from  electrolyte  and 
was  added  to  water  which  had  been  saturated  with 
H2S.  The  whole  was  sealed  in  a  flask  with  an  atmos- 
phere of  H2S. 

It  was  very  noticeable  that  in  the  absence  of  an  elec- 
trolyte the  CuS  remained  colloidal  and  dispersed,  and 
for  52  days  so  remained — no  clear  liquid  appearing 
above  the  precipitate.  On  the  53rd  day  it  was  noticed 
that  a  clear  layer  had  appeared.  In  a  few  days  the  pre- 
cipitated was  well  compacted  and  lay  on  the  bottom  of 
the  flask. 

At  the  end  of  75  days  the  flask  was  opened.  The 
black  precipitate  was  seen  with  the  miscroscope  to  be 
a -mass  of  well-compacted  particles  of  copper  sulfide 
which  were  mixed  with  particles  of  sulfur. 
'  This  precipitate  was  washed  with  water  and  alcohol 
and  then  partly  extracted  with  CS2.  The  CS2  gave 
much  sulfur  upon  evaporation. 

0.3921  g  of  the  residue  was  analysed  for  Cu  and 
forS.  It  gave  0. 1266  g  Sand  0.2655  gCu.  0.3921  g' 
Cu2S  yields  0.3178  g  Cu  and  the  same  weight  of  CuS 
yields  0.2606  g  Cu.  On  the  basis  of  the  copper  content 
of  the  residue  there  was  present  8.57%  Cu2S.  It  prob- 
ably contained  a  larger  percentage. 
H.rperiment  No.  16. — Attempt  to  produce  cuprous  sul- 
fide. 

TV — W.  H.  Emmons,  Bull.  529.  U.  S.  G.  S.  p  108. 


No.  2,  1914)      Clark — Chemistry  of  Coffer  Ore  Enrichment  JQ9 

100  cc  of  copper  sulfate  solution  and  100  cc  of  fer- 
rous sulfate  solution  (1  cc  equalling  0.33931  g  Cu  and 
1  cc  equalling  0.02624  g  Fe  respectively)  were  mixed, 
saturated  with  H2S  and  were  sealed  in  a  flask  with  an 
atmosphere  of  H2S. 

At  the  end  of  9  days  miscroscopic  particles  of  sulfur 
could  be  seen  on  the  side  of  the  flask.  At  the  end  of 
120  days  the  contents  of  the  flask  were  filtered  and  the 
residue  was  analysed.  The  residue  was  found  to  con- 
tain both  cuprous  and  cupric  sulfides. 

When  the  filtrate  was  neutralized  with  NaOH  a 
black  precipitate  of  copper  sulfide  came  down  with  the 
Fe(OH)2. 

Experiment  No.  //. — Production  of  cuprous  sulfide. 

100  cc  of  a  solution  of  copper  sulfate,  (1  cc  = 
0.039331  Cu),  was  saturated  with  SO2,  then  with 
H2S,  then  with  SO2  and  the  whole  sealed  in  a  flask 
with  an  atmosphere  of  SO2. 

At  the  end  of  1 1  days  the  flask  broke  inwardly.  The 
material  as  transferred  to  a  new  flask  and  given  a  new 
atmosphere  of  SO2  and  was  sealed. 

At  the  end  of  58  days  a  lump  raised  above  the  sur- 
face of  the  precipitate  to  the  height  of  one-half  inch  and 
caused  the  precipitate  to  appear  as  if  a  lump  of  ore 
were  embedded  in  it. 

This  lump  continued  to  grow,  and  another  came. 
From  the  first  lump  some  elevated  points,  suggestive  of 
horns,  struck  well  into  the  solution.  When  the  flask 
was  finally  opened  the  lumps  being  very  fragile  were 
destroyed.  One  of  the  "horns"  remained  whole  and 
under  the  microscope  was  seen  to  be  a  large  prism.  The 
residue  in  the  flask  consisted  of  black  copper  sulfide  and 
sulfur. 


HQ  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

When,  at  the  end  of  136  days,  the  flask  was  opened 
the  odor  of  SO2  could  not  be  observed. 

The  residue  was  analysed  after  having  been  washed, 
extracted  with  CS2,  etc.  0.7065  g  gave  0.1714  g  S 
thus  leaving  0.5351  g  Cu.  0.7065  g  of  Cu2S  contains 
0.5643  g  Cu  while  the  same  amount  of  CuS  contains 
0.4695  g  Cu.  On  the  basis  of  the  copper  content  the 
residue  was  69.16%  Cu2S. 

The  clear  supernatant  liquid  in  the  flask  was  filtered 
and  a  lump  of  zinc  was  added  to  the  filtrate.  A  very 
delicate  brownish  black  cloud  gathered  in  the  vicinity  of 
the  zinc.  This  was  considered  to  be  a  sulfide  of  Cu, 
(it  gave  a  strong  Cu  test),  which  had  been  held  in  solu- 
tion or  suspension  by  H2S,  (derived  probably  from  S), 
and  that  when  this  H2S  was  removed  by  the  partial 
pressure  of  the  H  from  the  zinc,  or  the  sulfide  was  pre- 
cipitated by  the  electrolytic  action  of  the  zinc,  this  cloud 
appeared. 
Experiment  No.  18. — Production  of  cuprous  sulfide  by 

the  use  of  sodium  thiosulfate. 

The  rapid  precipitation  of  Cu  by  amorphous  S  led 
to  the  suggestion  of  attempting  to  get  this  S  from  the 
decomposition  of  a  thiosulfate  as  Hillebrande1  seems  to 
have  found  thiosulfates  in  deep  mine  waters,  and  as 
Stokes11  had  shown  that  this  is  produced  when  alkaline 
solutions  act  on  pyrite. 

Three  flasks  were  taken  and  to  each  was  added  50  cc 
CuSO4  solution,  ( 1  cc  =  0.039331  g  Cu).  To  the  first 
was  added  5  cc  N/2  Na2  S2  O3,  to  the  second  25  cc  and 
to  the  third  50  cc  of  this  thiosulfate  solution.  Each 


I — 17th  Ann.  Rep.  U.  S.  G.  S.,  part  2,  p  21,  1896. 
II — H.  N.  Stokes,   "Experiments  on  the  action  of  various  so- 
lutions on  pyrite  and  marcasite".      Econ.   Geol.  2,  pp 
14-23,  1907. 


No.  2,  1914)       Clark— Chemistry  of  Cofttr  Ore  Enrichment  \\± 

flask  was  given  an  atmosphere  of  CO2  and  was  sealed. 

In  each  flask  the  double  thiosulfate  of  sodium  and 
copper  formed  at  once  and  then  began  to  decompose. 
The  contents  of  the  first  flask  were  black  in  2  days,  in 
the  second  flask  in  5  days  and  in  the  third  at  the  end. of 
several  weeks. 

The  formation  and  decomposition  of  the  double  thio- 
sulfate o'f  sodium  and  copper,  which  according  to  Du- 
toit111  has  the  copper  in  the  cuprous  condition,  goes  in 
several  steps  or  stages.  When  the  two  solutions  are 
mixed  tiny  yellow  prisms  are  formed.  These  on  stand- 
ing produced  long  yellow  needles  which  begin  to 
splinter,  even  going  so  far  as  to  be  a  mass  of  radiating 
splinters,  and  these  splinters  decompose  to  a  black  sul- 
fide,  decomposition  first  taking  place  at  the  end  of  the 
splinters. 

At  the  end  of  71  days  the  residue  in  the  second  flask 
was  washed  with  water  and  with  alcohol,  and  was  ex- 
tracted with  CS2  and  analysed.  0.5035  g  of  the  resi- 
due gave  0.1563  g  S  thus  leaving  0.3472  g  Cu. 

0.5035  g  Cu2S  contains  0.4022  g  Cu  and  this  amount 
of  CuS  contains  0.3347  g.     On  the  basis  of  the  copper 
content  this  residue  was  21.74%  Cu2S. 
Experiment  No.  /p. — The  effect  of  age  on  the  precipi- 
tating power  of  amorphous  sulfur. 

Early  in  this  work  it  was  noticed  that  freshly  pre- 
pared amorphous  sulfur  precipitated  copper  sulfide 
from  solutions  of  copper  sulfate  much  more  readily  than 
the  older  material. 

In  order  to  bring  out  this  fact  somewhat  quantita- 
tively H2S  and  SO2  were  brought  together  to  produce 
amorphous  sulfur.  This  when  free  from  the  gases  was 

III — Pierre  Dutoit,  "Sur  les  hyposulfltes  cupro  alkallns"  Jour, 
de  Chemie  Physique  2.  4,  pp  650-673,   1913. 


-L 

Curve  shouing  that  as  amorphous  sulfur  ages  It  can  precipi- 
tate smaller  amounts  of  copper  sulfide  from  a  sulfate 
solution  in  a  given  amount  of  time. 


No.  2,  1914)      C/ari — Chemistry  of  Co££er  Ore  Enrichment  \\% 

put  into  suspension  with  water  and  more  than  enough 
of  this  sulfur  to  precipitate  a  given  amount  of  copper 
from  a  sulfate  solution  was  added  to  each  of  seven 
bottles,  the  same  amount  being  added  to  each  bottle. 
A  given  amount  of  copper  sulfate  solution  was  added 
to  one  bottle  at  once,  to  a  second  at  the  end  of  24 
hours,  to  a  third  at  the  end  of  48  hours,etc.  Each  bot- 
tle was  then  shaken  and  allowed  to  stand  for  24  hours 
when  its  contents  were  filtered  and  analysed. 

The  results  of  the  experiment  are  shown  in  the  ac- 
companying curve. 
Experiment  No.  20. — Precipitating  power  of  pyrite  in 

various  solutions. 

With  a  view  of  ascertaining  those  conditions  most 
favorable  for  the  precipitation  of  Cu  as  a  sulfide  from 
CuSO4  solutions  by  means  of  pyrite,  and  with  a  view 
of  securing  more  data  on  the  role  of  SO2  a  given 
amount  of  200  mesh  pyrite  was  sealed  in  tubes  with  an 
aqueous  solution  of  CuSO4,  an  aqueous  solution  of 
CuSO4  saturated  with  SO2,  in  a  solution  of  CuSO4 
and  FeSO4,  in  a  solution  of  CuSO4  and  FeSO4  sat- 
urated with  SO2,  and  in  an  acidified  solution  of  CuSO4, 
(H2SO4  used)  which  was  isotonic  with  the  aqueous  so- 
lution which  had  been  saturated  with  the  SO2.  These 
tubes  were  shaken  once  daily  and  at  the  end  of  47  days 
their  contents  were  analysed. 

•  The  results  showed  that  the  amounts  of  copper  pre- 
cipitated increased  with  the  concentration  of  the  CuSO4 
solution,  that  great  precipitation  takes  place  in  aqueous 
solution,  and  that  this  is  increased  by  the  presence  of 
SO2.  The  results  also  showed  that  the  precipitation  in 
the  presence  of  FeSO4  is  not  as  great  as  in  its  absence, 
but  that  SO2  increases  this  precipitation  in  FeSO4. 
They  showed  that  the  reducing  action  of  SO2  and  not 
the  action  of  the  H  ion  is  responsible  for  the  increased 


BuJJttin  Univentty  of  New  Mtxtco      (Chem.  Ser.  Vol.  I 


precipitation  in  the  presence  of  this  substance.     More- 
over they  showed  that  neutrality  or  alkalinity  are  con- 
ditions most  favorable  for  precipitation. 
Details  are  given  in  the  following  table : 


1   g  pyrite 
22   cc 
liquid 
0.0787    g 
Cu   as 
CuS04 

1   g  pyrite 
24   cc 
liquid 
0.1573    g 
Cu   as 
CuSO4 

1   g  pyrite 
26   cc 
liquid 
0.2360    g 
Cu  as 
CuSO4 

1   g  pyrite 
28    cc 
liquid 
0.3146    g 
Cu  as 
CuSC) 


1 

2 

3 

4 

Amt.  Cu 

Amt.  Cu 

Amt.  Cu 

Amt.  Cu 

ppted 

ppted 

ppted 

ppted 

from 

from 

from 

from 

solution 

sol.  of 

N/10 

N/10 

of 

CuSO4 

FeSO. 

FeS04 

CuS04 

sat. 

sol.  of 

sol.  of 

with 

CuS04 

CuS04 

S02 

sat. 

with 

S02 

5 

Amt.  Cu 
ppted 
from 
H2S04 
sol.  of 
CuS04 

isotonic 
with 
sol.  in 

column 
2 


negligible 


Experiment  No.  21. — Precipitating  power  of  mono  and 
disulfides  and  of  mono  and  diarsenides. 

With  a  view  of  ascertaining  whether  disulfides  and 
diarsenides  would  precipitate  more  copper  than  the 
mono  compounds,  a  series -of  minerals  were  taken,  any 


No.  2,  1914)      CJarJc—  CA«mwtry  of  Cofar  Ort  Enrichment  U5 

impurities  removed  mechanically  as  far  as  possible,  and 
the  minerals  were  put  thru  a  200  mesh  sieve.  One 
gram  of  each  mineral  was  sealed  in  a  tube  with  an 
aqueous  solution  of  CuSO4,  each  tube  shaken  daily  and 
at  the  end  of  47  days  the  contents  were  analysed. 

As  a  result  of  this  experiment  it  was  concluded  that 
no  generality  was  shown.  Details  are  given  in  the 
table. 


I     s    f          !     | 

•§      »      I  ;  8      I     .i      »•     I      5      1;    ^ 

Amt.      .0916  .0916  .1374  .1374  .0916  .1374  .0916  .1374  .0916  .0916  .0916 
Cu  in 
25  cc 
solution 

Amt.      .0774  .0658  .1089  .0415  .0825  .1262  .0820  .1040  .0000  .0692  0726 

Cu  in 

nitrate 

Amt.      .0142  .0258  .0285  .0959  .0091  .0112  .0096  .0334  .0916  .0224  .0190 

Cu. 

ppted 

Experiment  No.  22. — Hydrogen  sulfidc  produced  by 
hydrolytic  action  of  water  on  pyrite. 

Several  one-half  gram  portions  of  uniform  sized 
pyrite  particles,  ranging  from  those  which  passed  thru 
the  20  mesh  sieve  and  were  retained  on  the  30  mesh  to 
those  which  passed  thru  the  200  mesh  sieve  were  sealed, 
each  portion  in  a  separate  tube,  with  20  cc  of  water. 

These  tubes  were  kept  at  about  41  degrees  for  three 
months,  when  the  tube  containing  the  80-90  mesh  py- 
rite was  opened,  its  contents  filtered  and  tested  colori- 
metrically  with  a  standard  solution  of  lead  nitrate.  The 
test  showed  the  presence  of  H2S  in  solution.  Other 
tubes  were  afterward  tested  and  their  contents  gave 
like  results. 


H6  Bulletin  Univer$iti,  of  New  Mextco      (Chem.  Ser.  Vol.  I 

Experiment  No.  23. — Production  of  hydrogen  sulfide 
from  pyritc,  chalcopyrite  and  bornite, 

Duplicate  tubes  containing : 

(a)  0.5  g  200  mesh  pyrite  and  15  cc  N/10  sulfuric 

acid 

(b)  0.5  g  200  mesh  chalcopyrite  and  15  cc  N/10  sul- 

furic acid 

(c)  0.5  g  200  mesh  bornite  and  15  cc  N/10  sulfuric 

acid 

were  sealed  and  placed  in  a  thermostat  at  about  41  de- 
grees for  51  days. 

The  contents  of  one  set  of  tubes  were  filtered  and 
the  filtrates  treated  with  standard  lead  nitrate  solu- 
tion. All  showed  the  presence  of  H2S  in  solution,  the 
pyrite  having  set  free  the  most  and  the  bornite  the 
least. 

The  duplicate  set  was  then  put  in  an  autoclave  and 
heated  at  195  degrees  for  two  hours.  The  tube  con- 
taining the  acid  and  pyrite  exploded,  the  one  containing 
the  acid  and  chalcopyrite  cracked  and  the  one  contain- 
ing the  acid  and  bornite  remained  intact,  tho  much 
pressure  was  developed  by  the  H2S  inside.  This  H2S 
was  readily  noticed  because  of  its  odor. 
Experiment  No.  24. — Cuprous  sulfide  from  the  double 

thiosulfate  of  sodium  and  copper. 

Some  of  the  double  thiosulfate  was  prepared  from 
solutions  of  copper  sulfate  and  sodium  thiosulfate.  This 
was  washed  and  sealed  in  a  flask  with  an  excess  of 
water  and  an  atmosphere  of  CO2. 

After  8  weeks  the  material  in  the  flask  began  to 
gather  into  large  platy  masses  which  stood  up  on  one 
edge  in  the  solution.  This  continued  until  the  material 
in  the  flask  was  well  compacted  into  large  platy  masses. 

The  flask  was  opened  at  the  end  of  123  days,  and  the 


No.  2,  1914)      Clark— Chemistry  of  Cofaer  Ore  Enrichment  U7 

residue  was  washed  with  water,  alcohol  and  was  dried 
and  extracted  with  CS2  and  analysed. 

0.5170  g  of  the  residue  gave  0.1380  g  S  thus  leav- 
ing 0.3790  g  Cu.  0.5170  g  of  Cu2S  contains  0.4130 
g  Cu,  while  this  weight  of  CuS  contains  0.3437  g  Cu. 
On  the  basis  of  the  copper  content  of  this  residue  it 
contained  50.94%  Cu2S. 
Experiment  No.  25.  - —  Attempt  to  precipitate  copper 

sulfide  by  the  use  of  coal. 

Lindgren,  Gratton  and  Gordon  think  that  coal  has 
acted  as  a  reducing  agent  on  copper  solutions  and  in 
their  "Ore  Deposits  of  New  Mexico"  show  a  beauti- 
fully colored  plate  of  chalcocite  embedded  in  coal. 

With  a  view  of  securing  data  on  this  method  of  pre- 
cipitation 2  grams  of  powdered  coal  were  put  into  a 
solution  of  CuSO4  and  FeSO4  and  the  whole  was  sat- 
urated with  SO2  and  sealed  in  a  flask.  Some  action 
was  expected  in  the  presence  of  these  three  reducing 
agents. 

The  flask  was  shaken  daily  and  at  the  end  of  122 
days  was  opened  and  its  contents  were  examined.  No 
deposition  of  sulfide  of  copper  was  observed. 

Great  care  was  taken  to  secure  a  coal  which  had  no 
pyrite  in  it.  The  results  of  this  experiment  seem  to 
indicate  that  carbon  alone  will  not  precipitate  the  sul- 
fide. Had  pyrite  been  present  in  the  coal  some  sulfide 
would  undoubtedly  have  been  precipitated. 
Experiment  No.  26. — Production  of  cuprous  sulfide. 

A  lump  of  chalcocite  weighing  2.2302  g  was  put  into 
a  solution  of  copper  sulfate,  (1  cc  =  0.039331  g  Cu), 
and  this  in  a  flask  was  connected  with  an  H2S  genera- 
tor so  that  the  H2S  was  always  present  in  the  flask. 


I — U.  S.   G.  S.  Prof.  Paper  No.   68,  p  67. 


113  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

The  H2S  was  not  passed  thru  the  liquid  but  was  al- 
lowed to  settle  upon  it. 

At  the  end  of  4  days  what  appeared  to  be  shining 
crystalline  faces  were  seen  on  the  lump  of  chalcocite, 
and  in  spite  of  the  precipitation  of  some  CuS  from  solu- 
tion the  liquid  appeared  to  be  more  blue  than  ever. 
This  latter  phenomenon  was  attributed  to  the  reflected 
color  of  covellite  films. 

At  the  end  of  100  days  the  flask  was  opened.  The 
chalcocite  was  found  to  weigh  1.9923  g — a  loss  of 
0.2379  g.  The  lump  was  badly  pitted. 

A  film  had  gathered  around  the  lump.  0.1083  g  of 
this  was  taken  for  analysis.  It  was  not  extracted  with 
CS2.  It  gave  0.0299  g  S  thus  leaving  0.0784  g  Cu. 

0.1083  g  Cu2S  contains  0.08648  g  Cu  while  the  same 
weight  of  CuS  contains  0.07197  g  Cu.  On  the  basis 
of  the  copper  content  of  the  film,  this  contained  43.1% 
Cu2S. 

Hard  films  of  the  CuS  which  had  originally  formed 
in  the  flask  could  be  separated  from  the  general  residue. 
These  were  washed,  extrated  pnd  analysed.  0.4718  g 
gave  0.1437  g  S  thus  leaving  0.3281  g  Cu.  0.4718  g 
Cu2S  contains  0.3768  g  Cu  and  the  same  weight  of 
CuS  contains  0.3135  g  Cu.  On  the  basis  of  the  copper 
content  this  film  was  23.07%  Cu2S. 

The  general  residue  in  the  flask  was  treated  as  de- 
scribed above  and  analysed.  0.6522  g  gave  0.2002  g  S 
and  0.4520  g  Cu.  Thus  the  Cu2S  content  of  the  gen- 
eral residue  was  21.28%. 

It  is  to  be  noted  that  the  chalcocite  lump  lost  weight, 
that  the  film  on  the  lump  was  richer  in  Cu2S  than  any 
other  part  of  the  material  in  the  flask,  and  that  the 
residue  near  the  film  was  richer  in  Cu2S  than  the  gen- 
eral residue.  Thus  we  see  the  tendency  of  the  Cu2S 
to  give  up  its  Cu  to  nearby  CuS,  (the  equilibrium  point 


No.  2,  1914)       Clark— Chemistry  of  Confer  Ore  Enrichment  H9 

we  do  not  know),  and  the  tendency  of  the  CuS  to  cFrop 
off  its  S  and  become  Cu2S,  or  because  of  the  dispersion 
of  the  chalcocite  the  material  nearest  to  the  lump  be- 
came most  contaminated  with  Cu2S. 
Experiment  No.  27. — Production  of  cuprous  sulfide. 

A  lump  of  pyrite  weighing  2.7769  g  was  placed  in  a 
flask  and  kept  under  conditions  as  described  under  ex- 
periment No.  26. 

At  the  end  of  one  week  a  color  and  luster  re- 
sembling covellite  was  noticeable. 

At  the  end  of  91  days  the  flask  was  opened.  The 
pyrite  weighed  2.7755  g — a  loss  of  0.0014  g. 

The  residue  was  washed,  dried,  extracted,  etc. 
0.9059  g  gave  0.1994  g  S  thus  leaving  0.7065  g  Cu. 
0.9059  g  Cu2S  would  give  0.7235  g  Cu  -and  the^same 
weight  of  CuS  would  give  0.6020  g  Cu.  On  the  basis 
of  the  copper  content  this  residue  contained  86.02% 
Cu2S. 
Experiment  No.  28. — Production  of  cuprous  sulfide. 

Under  conditions  as  described  for  Experiment  No. 
26,  1.8291  g  covellite  was  placed  in  contact  with  the 
sulfate  solution  and  the  H2S.  It  cannot  be  stated  just 
how  long  the  H2S  acted  on  the  solution  as  its  supply 
was  accidentally  interrupted. 

At  the  end  of  100  days  the  flask  was  opened.  The 
covellite  weighed  1.8241  g— a  loss  of  0.0050  g. 

The  residue  when  treated  as  described  showed  a  con- 
tent of  53.19%  Cu2S. 
Experiment  No.   29. — Production   of  cuprous  sulfide 

and  growth  on  bornite. 

Under  conditions  as  described  under  experiment 
No.  26,  4.2770  g  bornite  was  placed  in  a  flask  with  the 
copper  sulfate  solution  and  connected  with  the  H2S 
generator. 


120  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

At  the  end  of  one  week  the  color  and  luster  of  covel- 
lite  was  noticeable. 

At  the  end  of  94  days  the  flask  was  opened.  The 
lump  of  bornite  was  found  to  weigh  5.5569  g — a  gain 
of  0.2799  g.  This  growth  was  noticed  largely  in  the 
gain  in  weight  as  the  material  which  had  been  incorpo- 
rated with  the  lump  was  so  added  that  the  appearance 
of  the  lump  was  hardly  altered,  except  that  it  was  a 
deeper  dark  blue  than  usual.  This  experiment  seems  to 
indicate  that  the  copper  sulfide  tends  to  concentrate 
around  the  bornite.  Thus  bornite  could  turn  to  chalco- 
cite  thru  a  gradual  increase  in  its  copper  content. 

On  the  same  basis  (e.  i.,  copper  content)  as  stated 
in  Experiment  No.  26  the  residue  in  the  flask  was 
found  to  be  16.62%  Cu2S. 

Experiment  No.  jo. — Production  of  cuprous  sulfide. 

A  crystal  of  sphalerite  weighing  6.7795  g  was  placed 
in  a  flask  under  conditions  as  described  in  experiment 
No.  26. 

At  the  end  of  one  week  the  color  and  luster  of 
covellite  was  noticeable. 

At  the  end  of  93  days  the  flask  was  opened.  The 
lump  of  sphalerite  was  found  to  weigh  6.7745  g — a 
loss  of  0.0050  g,  yet  a  black  deposit  of  copper  sulfide 
hung  tenaceously  to  the  sphalerite  along  crystallo- 
graphic  lines.  The  whole  crystal  was  not  covered  with 
the  deposit.  It  seemed  that  the  sphalerite  is  an  excel- 
lent precipitant  of  the  sulfides  of  copper1  yet  that  in  the 
case  of  this  particular  sphalerite  crystal  only  a  portion 


I — Prof.  A.  F.  Rogers  of  Stanford  University  has  produced 
covellite  by  the  simple  heating  of  a  solution  of  CuSO4 
with  sphalerite  in  a  bomb  furnace.  School  of  Mines 
Quarterly,  32,  p  298,  1911. 


No.  2,  1914)      Clark—  Chemistry  of  Cofaer  Ore  Enrichment  121 

of  the  precipitated  sulfide  remained  on  the  sphalerite. 

The  residue  in  the  flask  was  treated  and  analysed  as 
has  been  already  described.    It  showed  a  Cu2S  content 
of  29.57%. 
Experiment  No.  31. — Production  of  cuprous  sulfide. 

(This  is  the  experiment  in  which  the  spontaneous 

change  of  CuS  to  Cu2S  and  S  was  first  noted.) 

A  solution  of  CuSO4  had  H2S  passed  thru  it  until 
all  the  copper  was  precipitated  as  the  sulfide.  The  pre- 
cipitate was  freed  from  solution  by  filtration  and  then 
this  precipitate  was  placed  in  a  flask  with  a  lump  of 
chalcocite  weighing  2.2861  g  and  the  whole  was  cov- 
ered with  water  and  sealed  an  an  atmosphere  of  CO2. 

After  54  days  the  flask  was  opened.  The  lump 
weighed  2,1404  g — a  loss  of  0.1457  g.  The  residue 
under  the  microscope  was  seen  to  be  made  up  of  par- 
ticles of  black  sulfide  which  were  intermingled  with 
particles  of  sulfur.  The  residue  was  extracted  with 
CS2  (which  was  known  to  be  free  from  dissolved  S) 
and  the  extract  evaporated.  A  yellow  .residue  which 
by  the  miscroscope  and  by  chemical  test  was  shown  to 
be  sulfur  was  left  upon  evaporation  of  the  CS2. 

The  residue  from  which  the  sulfur  had  been  extracted 
was  analysed  for  both  S  and  Cu,  and  upon  the  basis  of 
its  Cu  content  was  shown  to  be  43.64%  Cu2S.     Thus 
the  transformation  of  CuS  to  Cu2S  was  shown. 
Experiment  No.  32. — Production  of  cuprous  sulfide. 

A  suggestion  that  sodium  arsenite  can  transform 
CuS  to  Cu2ST  led  to  the  sealing  of  15  g  CuS  and  30  g 
sodium  arsenite  in  a  flask  with  an  atmosphere  of  CO2. 
200  cc  H2O  was  present. 

After  55  days  the  flask  was  opened  and  its  contents 

I — Gmelin-Kraut  "Handbuch  der  anorganische  Chemie"  Vol. 
5,  p   807. 


122  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

were    analysed.      They    showed    a    CuoS    content    of 
49.09%. 

This  transformation  was  at  first  attributed  to  the 
sodium  arsenite  but  in  view  of  spontaneous  changes 
obtained  in  other  experiments  the  amount  to  be  at- 
tributed to  each  cause  is  problematical. 
Experiment  No.  jj. — Growth  of  cuprous  sitlfide  on 

chalcocite. 

With  a  view  of  getting  some  experimental  cerifica- 
tion  of  the  formation  of  chalcocite  as  suggested  by 
Prof.  A.  F.  Rogers11  a  lump  of  chalcocite  weighing 
4.5240  g  was  put  into  a  flask  containing  CuS  and  a 
solution  of  K2S  which  had  been  completely  saturated 
with  H2S.  Testing  showed  that  this  liquid  held  con- 
siderable Cu  in  suspension  or  solution.  A  stopper 
with  a  Bunsen  valve  was  inserted,  thus  giving  the  H2S 
which  held  the  copper  in  suspension,  a  chance  to  escape. 

At  the  end  of  three  weeks  crystal  faces  were  seen 
shining  on  the  chalcocite  lump. 

At  the  end  of  85  days  the  flask  was  opened  and  the 
solution  displaced  by  water.  The  chalcocite  lump  was 
washed  with  hot  water  until  it  \vas  free  from  alkali. 
One  could  see  that  the  lump  was  coated  and  that  this 
coating  had  on  it  tiny  shining  spots  suggestive  of  crys- 
tal faces.  The  lump  was  dried.  It  weighed  4.5874  g — 
a  gain  of  0.0634  g.  32.24  milligrams  of  this  coating 
were  taken  for  analysis.  This  gave  8.403  mg  of  S, 
thus  leaving  23.837  mg  of  Cu.  32.24  mg  of  an  abso- 
lutely pure  chalcocite  would  give  25.748  mg  Cu. 

This  sulfur  figure  was  known  to  be  too  high.  \Yhile 
C.  P.  chemicals  were  used  a  very  noticeable  amount  of 
iron  oxide  was  detected  in  the  BaSO4  precipitate.  Fur- 
thermore, as  no  extraction  by  CS2  was  made  it  is  quite 

II — A.  F.  Rogers,   Econ.  Geol.   8.  p.   781,   1913. 


No.  2,  1914)      dark— Chemistry  of  Cofttr  Ore  Enrichment  123 

possible  that  a  small  amount  of  S  may  have  been  in  the 
material  deposited  on  the  chalcocite. 

The  author  has  no  hesitation  in  saying  that  he  pro- 
duced a  pure  chalcocite  from  this  alkaline  solution. 

The  analysis  of  the  residue  in  the  flask  showed  that 
it  had  a  Cu2S  content  of  57.63%. 

Experiment  No.  34. — Attempt  to  secure  miscroscopic 
evidence  of  the  change  of  covellite  to  chalcocite. 

H2S  was  passed  thru  a  solution  of  CuSO4  until  all 
the  copper  was  precipitated  as  a  sulfide,  then  some  200 
mesh  chalcocite  was  added  and  the  whole  was  sealed  in 
a  flask  with  an  atmosphere  of  CO2. 

A  similar  set  up  was  made  with  200  mesh  covellite. 

After  23  days  both  flasks  were  opened.  Their  con- 
tents showed  in  each  case  that  the  powdered  mineral 
was  embedded  in  the  amorphous  sulfide.  Free  sulfur 
was  noted  in  each  case.  Both  flasks  were  again  sealed 
with  CO2  atmospheres  and  both  were  opened  again  at 
the  end  of  113  days.  The  appearances  of  their  con- 
tents were  much  as  before,  except  that  a  much  larger 
amount  of  free  sulfur  could  be  seen. 

Experiment  No.  55. — Attempt  to  find  the  condition  of 
acidity  or  alkalinity  most  favorable  for  the  precipita- 
tion of  copper  sulfide  from  copper  sitlfatc  solutions 
by  means  of  pyrite. 

One  gram  of  200  mesh  pyrite  was  put  into  each  of 
1 1  tubes,  a  given  amount  of  CuSO4  was  added  to  each 
and  then  such  amounts  of  water  and  H2SO4  were  added 
as  to  have  the  acidity  of  the  solutions  in  the  different 
tubes  as  follows:  N/15,  N/20,  N/40,  N/80,  N/100, 
N/200  and  "neutral".  To  other  tubes  NaOH  and  water 
was  added  so  that  after  the  amount  of  NaOH  had  been 
added  which  would  theoreticallv  throw  down  all  of  the 


124  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

Cu  as  Cu(OH)2  the  alkalinity  of  the  tubes  was  N/200, 
N/100,  N/80,  N/40. 

The  contents  of  those  tubes  containing  the  alkali 
were  black  at  the  end  of  24  hours. 

Each  tube  was  shaken  once  daily  and  after  31  days 
the  contents  were  analysed. 

It  was  found  that  under  condition  of  acidity  there 
was  practically  no  copper  sulfide  precipitated. 

In  the  case  of  the  tubes  containing  the  alkali  the  dif- 
ficulty presented  itself  of  finding  out  how  much  of  the 
black  material  was  copper  oxide  and  how  much  was  a 
sulfide  of  copper.  It  seemed  reasonable  to  believe  that 
as  the  sulfide  precipitates  in  acidity  of  1 :8  HC1  that  if 
the  residue  were  washed  with  a  1 :10  HC1  the  sulfide 
would  not  be  dissolved.  This  proceedure  was  taken. 
All  of  the  material  dissolved,  thus  this  experiment 
proved  that  acidity  was  not  favorable  to  precipitation 
by  means  of  pyrite  but  left  the  question  as  to  alkalinity 
unsettled.  (See  also  Experiment  No.  20.) 

Experiment  No.  36. — Neutralising  power  of  different 
rocks. 

As  altered  rock  is  always  found  in  veins,  etc.,  show- 
ing downward  enrichment,  and  as  this  alteration  is  par- 
ticularly kaolinization,  and  as  experiments  No.  20  and 
35  indicated  that  acidity  is  not  favorable  to  the  deposi- 
tion of  the  sulfides  a  series  of  typical  rocks  was  taken 
and  the  neutralizing  effect  of  each  rock  on  acid  solution 
was  determined.  Each  rock  was  put  thru  a  200  mesh 
sieve.  5  grams  of  each  was  put  into  a  bottle  and  cov- 
ered with  50  cc  N/10  sulfuric  acid.  The  bottle  con- 
taining each  was  shaken  once  each  day.  After  30  days 
the  liquid  in  each  bottle  was  analysed. 


No.  2,  1914)       Clark— dentistry  of  Coffer  Ore  Enrichment 

Details  are  given  in  the  accompanying  table : 


125 


Rock    and 

Principal               Amt.  N/10 

Amt.  N/10         Relative 

Locality. 

minerals                      H2SO4 
in  order                        used 

H2SO4          neutralizing 
neutral-            power  of 

of 

ized               the  rock, 

abund- 

granite being 

ance 

taken  as  1. 

Franciscan 

Calcite                         50  cc 

48.5   cc                  10.32 

Limestone. 

Chalcedony 

Back    of 

Stanford 

University 

Basalt. 

Plagioclase                50  cc 

23.4  cc                    4.98 

Stanford 

Augite 

University 

Orthoclase 

Quarry. 

Zeolites 

Pyrite 

Diorite. 

Orothclase                  50   cc 

16.7   cc                    3.55 

Trinity 

(serecitized) 

River.      So. 

Hornblende 

Pork,    near 

Biotite 

Low   Gap,   Cal. 

Epidote 

Chlorite 

Franciscan 

Clay                              50   cc 

15.1  cc                    3.21 

Shale. 

substance 

Telsa, 

Quartz 

Cal. 

Fe    bearing 

minerals 

Rhyolite. 

Glass  (devlt-             50   cc 

11.0   cc                    2.34 

Alum   Rock, 

refled   and 

S.an    Jose, 

silicifled) 

Cal. 

Quartz   and 

Chalcedony 

Orthoclase 

Plagioclase 

Kaolin 

Iron   stain 

Hornblende 

Glass                            50  cc 

11.0  cc                    2.34 

Andeslte. 

Hornblende 

Marysville 

Plagioclase 

Cal. 

Orthoclase 

Granite. 

Orthoclase                 50   cc 

4.7                          1.00 

Santa 

Plagioclase 

Lucia, 

Quartz 

Cal. 

Biotite 

Apatite 

Experiment  No.  37. — Attempt  to  produce  cuprous  sul- 
fide. 
A  lump  of  pyrite  weighing  4.2663  g  and  some  care- 


126  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

fully  washed  CuS  were  put  into  a  solution  of  N/2 
K2CO3  and  the  whole  was  sealed  in  a  flask  with  an  at- 
mosphere of  CO2. 

At  the  end  of  95  days  the  flask  was  opened.  The 
pyrite  was  found  to  weigh  4.2653  g — a  loss  of  0.0010 
g.  The  pyrite  was  bright  and  shiny. 

The  residue  when  examined  with  the  miscroscope 
showed  that  some  sulfur  had  separated.  This  residue 
was  lost  in  the  process  of  analysis.  Judged  from  its 
appearance,  however,  this  residue  was  made  up  of  CuS 
with  a  small  amount  of  Cu2S. 

Some  iron  was  observed  in  the  liquid  contained  in 
the  flask. 
Experiment  No.  38. — Attempt  to  produce  cuprous  sul- 

fide  in  alkaline  solution. 

CuS  and  a  fairly  concentrated  solution  of  K2S  were 
heated  for  some  time,  finally  at  the  boiling  temperature 
of  the  solution.  The  liquid  was  allowed  to  settle  until 
clear.  The  clear  supernatant  solution  was  placed  in  a 
dessication  tube  over  sulfuric  acid,  and  this  tube  was 
evacuated  and  sealed. 

At  the  end  of  24  hours  a  brownish  mass  had  formed. 
This  with  the  hand  lense  had  the  appearance  of  a  lot  of 
tiny  needle-like  crystals.  With  high  magnification 
these  were  seen  to  be  long  curved  brownish  hairs.  When 
viewed  with  polarized  light  these  hairs  failed  to  show 
crystalline  characteristics.  Some  sulfur  could  be  seen 
along  with  these  hairs. 

The  liquid  in  the  dessication  tube  constantly  grew 
more  concentrated  as  the  sulfuric  acid  took  up  the  water 
vapor  and  at  the  end  of  113  days  these  were  seen  to  be 
masses  of  amorphous  copper  sulfide,  probably  cuprous 
as  other  experiments  showed. 


TST0.  2,  1914)       Clark—  Chemistry  of  Cofaer  Ore  Enrichment  12? 

Experiment  No.  ?p. — Solution  and  deposition  of  chal- 

cocite. 

Some  200  mesh  chalcocite  was  put  into  a  strong  so- 
lution of  KOH  and  H2S  was  passed  thru  the  solution, 
which  was  kept  cold,  until  the  solution  was  saturated. 
The  heavy  dense  chalcocite  became  collodial,  occupying 
4  or  5  times  its  original  volume.  This  whole  solution 
was  heated  in  an  autoclave  at  180  degrees  for  \l/2  hours. 
The  solution  became  deep  yellow.  This  was  filtered 
thru  glass  wool  and  was  then  gently  heated  on  an  air 
bath.  H2S  came  off  slowly  and  finally  black  lumps 
gathered  on  the  bottom  of  the  container. 

A  drop  of  this  filtrate  just  mentioned  was  evaporated 
on  a  glass  slide  and  its  residue  under  the  microscope 
showed  black  needles  or  prisms  together  with  some  yel- 
low prisms  suggestive  of  the  double  thiosulfate  of  so- 
dium and  copper.  Some  of  this  same  filtrate  was  neu- 
tralized with  dilute  sulfuric  acid  whereupon  a  brown- 
ish black  precipitate  was  formed.  This  gave  a  strong 
test  for  copper. 

Experiment  No.  40. — Solution  and  deposition  of  a  cop- 
per sulfide  derived  from  covellite,  bornite -and  chal- 
copyrite. 

Experiment  No.  39  was  repeated  with  each  of  the 
minerals  named  above. 

The  filtrate  from  covellite  behaved  as  did  the  filtrate 
obtained  in  No.  39.  A  few  of  the  hairs  as  obtained  in 
Experiment  No.  38  were  noted  on  the  glass  wrool  filter. 

The  filtrate  from  the  bornite  behaved  as  did  that 
from  the  covellite.  It  did  not  contain  as  much  copper, 
however.  A  larger  number  of  the  hairs  were  obtained 
from  the  bornite.  These  gave  a  very  strong  test  for 
copper. 


128  Bulletin  University  of  New  Mexico       (Chem.  Ser.  Vol.  I 

The  filtrate  from  the  chalcopyrite  gave  only  a  faint 
test  for  copper. 

It  appeared  that  the  H2S  had  dispersed  these  min- 
erals in  the  following  descending  order :  chalcocite,  cov- 
ellite,  bornite  and  chalcopyrite  and  that  the  alkaline 
liquid  with  its  H2S  had  dissolved  copper  from  these 
minerals  in  this  same  order. 

The  dispersion  and  solution  of  the  chalcocite  was 
much  more  marked  than  were  these  phenomena  with 
the  other  minerals. 
Experiment  No.  41. — Production  of  chalcocite  crystals, 

and  the  effect  of  hydrogen  sulfide  as  a  dispersing 

agent. 

2  grams  of  200  mesh  chalcocite  were  put  into  a  tall 
Nessler  tube  and  covered  with  25  cc  of  a  KHS  solu- 
tion. H2S  was  passed  thru  the  solution  for  an  hour. 

The  same  amount  of  chalcocite  was  put  into  a  tube 
and  covered  with  25  cc  of  a  K2S  solution.  Hydrogen 
was  passed  thru  this  solution  for  an  hour. 

The  same  amount  of  chalcocite  was  put  into  another 
tube  and  was  covered  with  25  cc  of  a  solution  of  equal 
parts  of  K2S  and  KOH.  Hydrogen  was  passed  thru 
this  liquid  for  an  hour. 

Each  solution  contained  approximately  the  same 
amount  of  potassium.  The  gases  were  passed  thru  the 
liquids  at  approximately  equal  rates. 

The  material  in  the  first  tube  showed  strong  disper- 
sion, that  in  the  second  showed  l/4th  to  l/6th  as 
much  and  that  in  the  third  showed  scarcely  any. 

At  the  end  of  10  days  it  was  noted  that  the  material 
in  the  second  tube  had  risen,  and  that  a  small  mass  hav- 
ing something  of  a  crystalline  appearance  floated  on 
the  surface.  From  this  hung  clown  a  growth  resem- 
bling a  fox's  tail. 


No.  2,  1914)      Clark— Chemistry  of  Co££er  Ore  Enrichment  129 

This  growth  and  "tail"  were  washed,  and  the  latter 
examined  with  a  microsscope.  This  "tail"  was  seen 
to  be  made  up  of  a  lot  of  stiff  black,  non-transparent 
hairs  or  rods.  One  or  two  were  especially  large  end 
showed  truncated  ends.  The  angles  on  the  ends  of  one 
rod  were  measured.  Beginning  on  the  right  side  of  the 
rod  or  prism  and  going  anti-clock  wise  the  angles  were 
approximately  37,  51  and  56  degrees.  (See  figure.) 

The  floating  mass  was  washed  again  with  water  and 
with  absolute  alcohol  and  was  then  dried.  It  was 
found  to  weight  13  mg.  It  was  analysed  with  the 
greatest  care  and  was  found  to  yield  2.57  mg  S  and 
10:40  mg  Cu.  13  mg  of  Cu2S  would  yield  10.39  mg 
Cu.  The  floating  mass  was  certainly  cuprous  sulfide. 
The  author  assumes  that  the  crystals  were  of  the  same 
composition. 
Experiment  No.  42. — Elimination  of  iron  from  bornite. 

Work  done  simultaneously  with  this  by  Tolman  and 
Ray  has  shown  that,  from  microscopic  evidence,  we 
m?y  believe  that  bornite  gives  off  some  of  its  iron  and 
becomes  chalcocite. 

With  a  view  of  actually  securing  some  data  on  this 
idea  samples  of  bornite  were  analysed  for  their  iron 
contents.  These  powdered  samples  were  placed  in 
water  in  sealed  tubes  and  were  heated  in  an  autoclave 
at  a  temperature  of  about  175  degrees  for  two  hours. 

The  contents  of  the  tubes  were  filtered  and  the  resi- 
dues were  washed  with  N/10  sulfuric  acid  as  this  acid 
•does  not  attack  bornite  to  any  appreciable  extent. 

The  filtrates  and  washings  gave  strong  iron  tests. 

Quantitative  tests  were  not  made. 

Experiment  No.  43. — The  dispersing  pou'er  of  hydro- 
gen snlfide  in  acid  solution. 
To  determine  the  dispersing  power  (relative),  in  acid 


130  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

solution  four  gas  washing  bottles  were  taken.  To  the 
first  2  grams  of  200  mesh  chalcocite  was  added,  to  the 
second  2  grams  of  200  mesh  covellite,  to  the  third  bor- 
nite  and  to  the  fourth  chalcopyrite.  50  cc  of  N/10 
sulfuric  acid  \vas  added  to  each  bottle.  H2S  was  passed 
thru  the  4  bottles  for  a  few  minutes  each  day  for  4 
weeks. 

At  the  end  of  this  time  all  the  minerals  were  slightly 
dispersed,  this  dispersion  appearing  most  in  the  chalco- 
cite and  least  in  the  chalcopyrite. 

The  contents  of  the  bottles  were  filtered.  All  of  the 
filtrates  appeared  clear,  tho  that  from  the  chalcocite 
gave  the  merest  suggestion  of  being  less  clear  than  the 
others. 

Lumps  of  zinc  were  added  to  each  filtrate.  In  the 
chalcocite  filtrate  a  brownish  black  cloud  appeared  at 
once  around  the  zinc.  This  cloud  did  not  appear  in 
the  others  tho  they  became  less  clear. 

The  residues  which  were  left  in  the  tubes  containing 
the  filtrates  after  the  zinc  had  gone  into  solution  were 
dissolved  in  nitric  acid  and  this  acid  was  more  than  neu- 
tralized with  NH4OH.  All  showed  traces  of  copper 
the  test  being  strongest  in  the  residue  from  the  chalco- 
cite filtrate  and  least  in  that  from  the  chalcopyrite.  A 
very  noticeable  amount  of  Fe(OH).?  was  observed  in 
the  tube  containing  the  residue  from  the  bornite  filtrate. 

This  experiment  showed  clearly  that  H2S  disperses 
these  minerals  in  acid  solution  and  that  the  dispersion 
is  in  a  measure  proportional  to  their  copper  content.  It 
also  shows  that  in  acid  solution  and  in  contact  with 
H2S  bornite  gives  up  some  of  its  iron. 

Dispersion  in  acid  solution  is  very  much  less  then  in 
alkaline. 


No.  2,  1914)       Clark— Chemistry  of  Cofaer  Ore  Enrichment  131 

Experiment  No.  44. — Order  of  dispersion  of  minerals 

in  alkaline  solution. 

Under  conditions  as  described  in  experiment  No.  43 
chalcopyrite,  bornite,  enargite,  covellite  and  chalcocite 
were  covered  with  dilute  KHS  and  were  treated  with 
H4S  for  4  days.  All  dispersed.  An  attempt  was  made 
to  show  that  the  iron  to  copper  ratio  in  the  dispersed 
material  was  less  than  in  the  mineral  from  which  the 
material  was  dispersed.  Because  of  limited  time  colori- 
metric  methods  were  used.  These  were  not  suitable 
because  of  the  iron  content  of  even  the  best  reagents. 
This  experiment  did  show  that  these  minerals  were  dis- 
persed in  the  reverse  order  as  given,  and  dispersed  in 
such  a  finely  divided  form  that  the  material  readily 
tvent  thru  a  filter.  This  dispersion  was  very  strong. 

SUMMARY. 

\Yhile  the  work  included  in  this  present  paper  has 
been  largely  exploration  along  a  variety  of  lines,  and 
while  it  can  scarcely  be  said  that  the  investigation  ha's 
been  carried  in  any  particular  direction  to  such  an  ex- 
tent as  to  ultimately  determine  with  quantitative  ac- 
curacy the  importance  of  the  various  factors  studied  in 
respect  to  the  enrichment  of  sulf  ide  ores,  it  seems  never- 
theless true  that  certain  heretofore  little  understood 
and  in  many  cases  unsuggested  processes  do  enter  into 
the  general  problem  of  the  chemistry  of  the  enrichment 
of  the  sulfide  ores  of  copper.  Perhaps  the  whole  re- 
sults may  be  summarized  in  the  following  general 
statements : 


132  Bulletin  University  of  New  Mexico       (Chem.  Ser.  Vol.  I 

( 1 )  Enrichment  does  not  necessarily  depend  upon 
oxidation  and  leaching  processes  and  upon  the  forma- 
tion of  electrolytic  solutions  of  copper,  such  as  the  sul- 
fate  or  chloride,  but  may  perfectly  well  occur  thru  the 
intervention  of  the  colloidal  dispersion  and  solution, 
and  subsequent  deposition,  either  in  the  amorphous  or 
crystalline  form  of  already  existing  sulfides  of  copper. 
This  applies  to  upward  enrichment. 

(2)  The  most  effective  dispersing  agent  which  is 
likely  to  be  found  in  nature  is  hydrogen  sulfide,  which 
may  be  produced  in  a  variety  of  ways,  notably  from 
any  sulfide  minerals  by  contact  with  dilute  acids  or 
even  with  pure  water.     It  is  probably  assisted  by  car- 
bon dioxide. 

The  spontaneous  dispersion  of  already  existing  sul- 
fides is  least  in  acid  solutions  and  enormously  greater 
in  alkaline  solution,  from  which  it  is  to  be  expected  that 
such  operations  will  be  of  greater  importance  at  con- 
siderable depth. 

Free  sulfur  may  also  serve  as  a  dispersing  agent, 
and  the  same  is  true  of  higher  sulfur-bearing  minerals) 
as  pyrite,  which  acts  to  all  intents  and  purposes  as  po- 
tential sulfur. 

(3)  The  conditions  favorable  to  the  deposition  of 
dispersed  copper  sulfides  are  the  removal  or  absorption 
of  the  dispersing  agent.  Thus  loss  of  hydrogen  sul- 
fide from  a  colloidal  suspension  of  sulfides  of  copper 


No.  2,  1914)       Clark— Chemistry  of  Co££er  Ore  Enrichment  133 

tends  to  flocculate  and  precipitate  these  sulfides.  The 
condition  for  the  appearance  of  crystalline  rather  than 
amorphus  deposits  seems  to  be  the  fairly  complete  re- 
moval of  hydrogen  sulfide  which  is  readily  accom- 
plished by  sulfur  dioxide  which  accounts  for  the  suc- 
cess of  the  Winchell-Tolman  experiments. 

(4)  There  seems  to  be  no  doubt  but  that  cuprous 
sulfide  (chalcocite)  is  the  most  stable  of  all  of  the  cop- 
per sulfide  minerals,  in  contact  with  solution,  at  least, 
and  that  there  will  be  a  general  tendency  for  all  copper 
sulfide-bearing  minerals  to  eliminate  cuprous  sulfide, 
and  for  all  sulfide  precipitates  from  electrolyte  solutions 
to  spontaneously  go  over  into  the  cuprous  form.  This 
tendency  may  possibly  be  more  or  less  hampered  by  the 
presence  of  an  excess  of  sulfur,  such  sulfur  may  tho 
be  gradually  eliminated  by  solution  in  alkaline  waters, 
and  even  by  reaction  with  pure  water,  and  transporta- 
tion to  long  distances  may  be  accomplished. 

Thus  in  the  following  figure,  (diagramatic),  if  AB 
represents  a  mass  of  sulfide-bearing  ore,  and  alkaline 
waters  charged  with  hydrogen  sulfide  gradually  perco- 
late from  B  toward  A,  there  will  occur  first  a  zore  of 
dispersion  (Zone  2).  Upon  elimination  or  absorption 
of  hydrogen  sulfide,  there  will  follow  a  zone  of  amor- 
phous chalcocite  enrichment  (Zone  3). 

Following  this  with  more  complete  elimination  of 
hydrogen  sulfide.  accomplished  perhaps  by  the  appear- 


134 


Bulletin  University  of  New 


(Chem.  Ser.  Vol.  I 


ance  of  sulfur  dioxide  as  a  result  of  limited  oxygen 
supply,  crystalline  chalcocite  will  appear,  (Zone  4). 


Appearance  of  SO2  thru  small 
supply  of  O2.  Deposit  of  crys- 
talline chalcocite. 


Deposit  of   amorphous   chalcocite 
changing   to   massive. 


Zone   of   dispersion. 


Alkaline    water    charged    with    H.,S. 


Zone   3          Copper 
.         Sulflde 


(5)  There  seems  to  be  also  a  curious  physical  effi- 
nity  on  the  part  of  the  chalcocite  to  draw  toward  itself 
any  freshly  formed  cuprous  sulfide,  and  to  cause  amor- 
phous deposits  of  the  new  sulfide  on  the  already  present 
chalcocite.  Already  present  chalcocite  may  also  seem- 
ingly exert  a  sort  of  induced  acceleration  on  the  reac- 
tion between  electrolytic  solution  of  copper  salts  and 
free  sulfur,  resulting  in  the  ultimate  formation  of  chal- 
cocite. (See  Experiment  Xo.  13.) 


APPENDIX. 

After  the  author  had  finished  the  experimentation 
which  led  to  the  conclusions  given  in  this  paper,  there 
remained  many  questions  bearing  on  this  work  which 


No.  2,  1914)       Clark— Chemistry  of  Co££er  Ore  Enrichment  lg§ 

still  needed  explanation.  Time  was  not  available  for 
anything  like  a  complete  investigation  of  these  questions 
but  the  author  was  able  to  make  some  interesting  ex- 
periments which  are  suggestive.  Since  the  conclusions 
as  derived  from  these  experiments  have  only  a  sugges- 
tive value  the  conclusions  and  the  experiments  are  here 
given  in  this  appendix. 

In  this  paper  it  has  been  shown  that  copper  sulfide 
is  kept  colloidal  by  hydrogen  sulfide  and  with  hydro- 
gen sulfide  the  colloid,  (or  colloids),  migrate  very 
readily.  Naturally  the  question  arose  as  to  whether  this 
dispersion  and  migration  would  be  assisted  or  retarded 
by  carbon  dioxide,  which  is  known  to  be  present  in 
many  of  the  springs  which  give  off  hydrogen  sulfide, 
and  it  is  found  in  some  mine  gases  which  are  given  off 
from  the  cracks  in  the  wall  rocks  of  the  mines.  Quite 
naturally,  too,  it  was  asked  whether  some  solutions 
would  favor  dispersion  and  whether  others  would  tend 
to  flocculate  the  colloidal  copper  sulfide.  What  effect 
would  certain  wall  substances  have  on  the  colloid? 
Moreover  it  has  been  asked  very  frequently,  what  be- 
comes of  sulfur  if  such  at  any  time  be  set  free  in  the 
process  of  ore  deposition. 

One  sees  in  experiments  No.  45,  No.  46,  and  No.  47 
some  interesting  facts  which  suggest  possible  answers 
to  these  questions. 

We  notice  here  that  those  solutions  containing  small 


136  Bulletin  Univtr$ity  of  New  M ext'co      (Chem.  Ser.  Vol.  I 

amounts  of  sodium  and  potassium  salts  are  most  favor- 
able for  the  dispersion  of  the  colloidal  copper  sulfide, 
and  believe  that  our  deep-seated  ore  solutions  actually 
are  rich  in  potassium.  We  see  that  calcium  and  alum- 
inium salts  coagulate  the  colloidal  copper  sulfide  and 
notice  particularly  that  even  the  most  insoluble  alum- 
inium compound,  (dehydrated  aluminium  oxide),  is 
exceedingly  effective  as  a  flocculant.  We  notice  that 
calcium  carbonate  flocculates  the  colloid  but  that  in  the 
case  of  this  colloidal  copper  sulfide  being  precipitated 
by  calcium  carbonate  the  colloid  may  be  slightly  dis- 
persed again  by  means  of  hydrogen  sulfide,  some  cal- 
cium going  into  solution,  altho  this  dispersion  is  by  no 
means  as  great  as  in  the  presence  of  alkali  salts. 

If  one  makes  but  a  hasty  examination  of  a  good 
treatise  on  ore  deposits*  he  will  notice  many  examples 
of  copper  sulfide  deposits  embedded  in  limestone,  some 
of  the  limestone  having  been  replaced,  and  he  will  find 
that  equally  numerous  are  the  data  showing  copper 
sulfide  deposits  in  contact  with,  and  embedded  in,  shale, 
gouge  or  other  argillaceous  material.  May  not  the  re- 
sults of  these  experiments  partially  account  for  such 
deposits  ? 

As  is  shown  in  Experiment  No.  46,  carbon  dioxide 
is  a  most  excellent  agent  for  dispersing  colloidal  sulfur. 


* — Very  strikingly  shown  in   many   illustrations   in   Lindgren, 
"Mineral  Deposits". 


No.  2,  1914)      CJart— Chemistry  of  Cofaer  Ore  Enrichment  \^J 

tho,  as  the  author  has  found,  it  assists  the  dispersion 
of  copper  sulfide  when  hydrogen  sulfide  is  present  and 
precipitates  the  copper  sulfide  when  hydrogen  sulfide  is 
absent.  We  may  not  think  that  carbon  dioxide  has 
aided  in  bringing  the  copper  sulfide  up  to  where  it  is 
deposited,  has  caused  the  colloidal  sulfide  to  flocculate 
when  the  hydrogen  sulfide  has  escaped,  has  been  as- 
similated or  has  ceased  to  flow,  and  then  having  caused 
the  copper  sulfide  to  deposit,  the  carbon  dioxide  has 
carried  on  any  excess  sulfur  to  be  used  up  in  pyritiza- 
tion  of  the  surrounding  country  rock  and  perhaps  in 
many  other  ways  ? 

More  thorogoing  investigation  of  all  the  lines  sug- 
gested in  this  paper  will  be  pushed  forward  as  rapidly 
as  possible. 

Experiment  No.  45. — Plocculatwn  of  colloidal  copper 

sulfide. 

Some  colloidal  copper  sulfide  was  prepared,  and  by 
washing  was  carefully  freed  from  the  presence  of  any 
electrolyte. 

Equal  portions  of  this  colloidal  material  were  put 
into  flasks  and  were  treated  with  dilute  solutions  of 
NaCL  KC1,  CaCL,  and  A1C13  and  with  powdered 
CaCO3  and  A12O3  in  water  as  can  be  seen  in  detail  in 
the  accompanying  table. 

It  was  found  that  the  presence  of  NaCl  and  KC1  in- 
creased the  amount  of  the  sulfide  which  was  held  in  sus- 
pension, whereas  CaCl2,  CaCO3,  A1C13,  and  A12O3 
caused  the  colloid  to  flocculate.  This  flocculation  was 
accomplished  very  rapidly  by  the  A12O;J. 


138  Bulletin  Univer$ity  of  New  Mexico      (Chem.  Ser.  Vol.  I 

A  similar  set  of  solutions  with  the  colloidal  sulfide 
were  treated  with  H2S.  The  hydrogen  sulfide  increased 
the  amount  of  material  which  was  held  in  suspension 
by  water,  Nad  solution  and  KC1  solution.  Also  it  car- 
ried into  suspension  some  copper  sulfide  which  had 
been  flocculated  at  CaCO3,  thus  indicating  that  tho 
limestone  may  tend  to  precipitate  copper  sulfide  from 
ore  solutions  having  this  in  suspension,  the  colloids  in 
the  presence  of  H2S  may,  to  some  extent  at  least,  mi- 
grate thru  limestone.  The  H2S  failed  to  disperse  the 
colloid  which  had  been  precipitated  by  CaCl2,  A1C13, 
and  A12O3. 

A  similar  set  of  solutions  with  the  colloidal  copper 
sulfide  were  treated  with  a  mixture  of  H2S  and  CO2. 
The  results  were  much  as  those  produced  with  the  H2S 
alone,  except  that  not  as  much  of  the  colloid,  which  had 
been  precipitated  by  the  CaCO3  was  again  put  into  sus- 
pension, which  could  be  accounted  for  by  the  fact  that 
the  CO2  acting  on  the  carbonate  undoubtedly  produced 
calcium  ions. 

This  experiment  showed  most  strikingly  the  great 
tendency  of  argillaceous  material  to  flocculate  colloid 
copper  sulfide. 


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No.  2,  1 9 1 4  )      Clark—  Chemistry  of  Coffcr  Or.  EnricJimtnt  J41 

Experiment  No.  47. — Dispersing  and  flocculating  ef- 
fects of  H2S}  SO2,  and  C02  on  colloidal  copper  sul- 
fide  and  on  colloidal  sulfur,  in  water  and  in  the  pres- 
ence of  A71400  K2CO?  and  KCl. 
A  colloidal  copper  sulfide  was  prepared  as  described 
in  Experiment  No.  45.    A  colloidal  sulfur  solution  was 
prepared  by  the  action  of  H2S  on  SO2,  the  sulfur  being- 
suspended  in  water. 

Portions  of  each  colloidal  solution  were  saturated 
with  H2S,  SO2,  and  CO2,  and  then  portions  to  which 
K2CO3  and  KCl  had  been  added  so  that  the  K  ion  was 
N/1400,  were  saturated  with  the  gases. 
The  results  are  here  tabulated. 


Water  suspension 
of  the 
Colloid 

N/1400    K,CO3    and    KCl 
suspension    of   the 
Colloid. 

H2S 

H2S   caused   the 

sulfur    to    flocculate 
rapidly.                             , 

H2S   caused   the 
sulfur   to   flocculate 
slowly. 

S02 

SO2  did  not 
flocculate    the    sulfur 
rapidly. 

SO2   did   not 

flocculate    the   sulfur 
rapidly. 

C02 

CO2   practically 
prevented    the 
flocculation   of  the 
sulfur. 

CO2  prevented   the 
flocculation   of   the 
sulfur. 

COPPER    SUI.FIDE 


Water    suspension    of 
the    Colloid. 

N/1400   K2CO.t  and  KCl 
suspension  of 
the   Colloid. 

H2S 

H2S   kept   the 
copper   sulflde 
dispersed    for   a   long 
time. 

H0S  practically  prevented 
any  flocculation   of   the 
copper   sulflde. 

so2 

SO,   caused   the 
copper   sulflde    to 
flocculate. 

SO2   caused    the 
copper   sulflde   to 
flocculate. 

CO2 

CO2  caused   a 
very  clean  cut 
flocculation  of  'the 
copper    sulflde. 

CO2    caused    a 
very  clean   cut 
flocculation   of   the 
colloid. 

142  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

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This  work  was  undertaken  in  the  hope  of  giving 
more  information  to  the  geologist,  and  in  some  de- 
gree it  has  been  successful. 

The  amount  of  success  which  has  attended  the  ef- 
forts of  the  writer  is  in  no  small  degree  due  to  the  in- 
terested suggestion,  assistance  and  oversight  given  by 


15(J  Bulletin  University  of  New  Mexico      (Chem.  Ser.  Vol.  I 

Professors  C.  F.  Tolman,  Jr.,  A.  F.  Rogers  and  S.  W. 
Young.  Professor  Tolman  indicated  geological  inter- 
pretations of  the  work,  Professor  Rogers  contributed 
most  willingly  many  of  his  finest  mineral  specimens  for 
experimentation  and  Professor  Young  gave  direct  su- 
pervision of  the  research.  To  these  gentlemen,  and 
particularly  to  Professor  Young,  the  author  acknow- 
ledges his  deep  indebtedness. 

JOHN  DUSTIN  CLARK. 

Leland  Stanford  Junior  University, 
May  18th,  1914. 


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